Security issues:

• Fixed ReDOS vulnerability in mpmathify() (CVE-2021-29063) (Vinzent Steinberg)

Features:

• Added quadsubdiv() for numerical integration with adaptive path splitting
  (Fredrik Johansson)
• Added the Cohen algorithm for inverse Laplace transforms
  (Guillermo Navas-Palencia)
• Some speedup of matrix multiplication (Fredrik Johansson)
• Optimizations to Carlson elliptic integrals (Paul Masson)
• Added signal functions (squarew(), trianglew(), sawtoothw(), unit_triangle()
  sigmoidw()) (Nike Dattani, Deyan Mihaylov, Tina Yu)

Bug fixes:

• Correct mpf initialization from tuple for finf and fninf (Sergey B Kirpichev)
• Support QR decomposition for matrices of width 0 and 1 (Clemens Hofreither)
• Fixed some cases where elliprj() gave inaccurate results (Fredrik Johansson)
• Fixed cases where digamma() hangs for complex input (Fredrik Johansson)
• Fixed cases of polylog() with integer-valued parameter with complex type
  (Fredrik Johansson)
• Fixed fp.nsum() with Euler-Maclaurin algorithm (Fredrik Johansson)

Maintenance:

• Dropped support for Python 3.4 (Sergey B Kirpichev)
• Documentation cleanup (Sergey B Kirpichev)
• Removed obsolete files (Sergey B Kirpichev)
• Added options to runtests.py to skip tests and exit on failure
  (Jonathan Warner)