Erlang PostgreSQL Database Client
* Connect
  {ok, C} = pgsql:connect(Host, [Username], [Password], Opts).
  Host      - host to connect to.
  Username  - username to connect as, defaults to $USER.
  Password  - optional password to authenticate with.
  Opts      - property list of extra options. Supported properties:
    + {database, String}
    + {port,     Integer}
    + {ssl,      Atom}       true | false | required
    + {ssl_opts, List}       see ssl application docs in OTP
    + {timeout,  Integer}    milliseconds, defaults to 5000
    + {async,    Pid}        see Asynchronous Messages section
  {ok, C} = pgsql:connect("localhost", "username", [{database, "test_db"}]).
  ok = pgsql:close(C).
  The timeout parameter will trigger an {error, timeout} result when the
  server fails to respond within Timeout milliseconds. This timeout applies
  to the initial connection attempt and any subsequent queries.
* Simple Query
  {ok, Columns, Rows}        = pgsql:squery(C, "select ...").
  {ok, Count}                = pgsql:squery(C, "update ...").
  {ok, Count, Columns, Rows} = pgsql:squery(C, "insert ... returning ...").
  {error, Error}             = pgsql:squery(C, "invalid SQL").
  Columns       - list of column records, see pgsql.hrl for definition.
  Rows          - list of tuples, one for each row.
  Count         - integer count of rows inserted/updated/etc
  The simple query protocol returns all columns as text (Erlang binaries)
  and does not support binding parameters.
* Extended Query
  {ok, Columns, Rows}        = pgsql:equery(C, "select ...", [Parameters]).
  {ok, Count}                = pgsql:equery(C, "update ...", [Parameters]).
  {ok, Count, Columns, Rows} = pgsql:equery(C, "insert ... returning ...", [Parameters]).
  {error, Error}             = pgsql:equery(C, "invalid SQL", [Parameters]).
  Parameters    - optional list of values to be bound to $1, $2, $3, etc.
  The extended query protocol combines parse, bind, and execute using
  the unnamed prepared statement and portal. A "select" statement returns
  {ok, Columns, Rows}, "insert/update/delete" returns {ok, Count} or
  {ok, Count, Columns, Rows} when a "returning" clause is present. When
  an error occurs, all statements result in {error, #error{}}.
  PostgreSQL's binary format is used to return integers as Erlang
  integers, floats as floats, bytea/text/varchar columns as binaries,
  bools as true/false, etc. For details see pgsql_binary.erl and the
  Data Representation section below.
* Parse/Bind/Execute
  {ok, Statement} = pgsql:parse(C, [StatementName], Sql, [ParameterTypes]).
  StatementName   - optional, reusable, name for the prepared statement.
  ParameterTypes  - optional list of PostgreSQL types for each parameter.
  For valid type names see pgsql_types.erl.
  ok = pgsql:bind(C, Statement, [PortalName], ParameterValues).
  PortalName      - optional name for the result portal.
  {ok | partial, Rows} = pgsql:execute(C, Statement, [PortalName], [MaxRows]).
  {ok, Count}          = pgsql:execute(C, Statement, [PortalName]).
  {ok, Count, Rows}    = pgsql:execute(C, Statement, [PortalName]).
  PortalName      - optional portal name used in bind/4.
  MaxRows         - maximum number of rows to return (0 for all rows).
  execute returns {partial, Rows} when more rows are available.
  ok = pgsql:close(C, Statement).
  ok = pgsql:close(C, statement | portal, Name).
  ok = pgsql:sync(C).
  All functions return {error, Error} when an error occurs.
* Data Representation
  null        = null
  bool        = true | false
  char        = $A | binary
  intX        = 1
  floatX      = 1.0
  date        = {Year, Month, Day}
  time        = {Hour, Minute, Second.Microsecond}
  timetz      = {time, Timezone}
  timestamp   = {date, time}
  timestamptz = {date, time}
  interval    = {time, Days, Months}
  text        = <<"a">>
  varchar     = <<"a">>
  bytea       = <<1, 2>>
  array       = [1, 2, 3]
  record      = {int2, time, text, ...} (decode only)
* Errors
  Errors originating from the PostgreSQL backend are returned as {error, #error{}},
  see pgsql.hrl for the record definition. epgsql functions may also return
  {error, What} where What is one of the following:
  {unsupported_auth_method, Method}     - required auth method is unsupported
  timeout                               - request timed out
  closed                                - connection was closed
  sync_required                         - error occured and pgsql:sync must be called
* Asynchronous Messages
  PostgreSQL may deliver two types of asynchronous message: "notices" in response
  to notice and warning messages generated by the server, and "notifications" which
  are generated by the LISTEN/NOTIFY mechanism.
  Passing the {async, Pid} option to pgsql:connect will result in these async
  messages being sent to the specified process, otherwise they will be dropped.
  Message formats:
    {pgsql, Connection, {notification, Channel, Pid, Payload}}
      Connection  - connection the notification occured on
      Channel     - channel the notification occured on
      Pid         - database session pid that sent notification
      Payload     - optional payload, only available from PostgreSQL >= 9.0
    {pgsql, Connection, {notice, Error}}
      Connection  - connection the notice occured on
      Error       - an #error{} record, see pgsql.hrl