Misc fixes

[skirpichev]

• add mpfr_nrandom(), pack() and unpack() to sphinx docs
• fix formatting & add refs to history.rst
• update docs/intro.rst & versions info
• adapt some headers in prose docs

[codecov-commenter]

Codecov Report

Merging #412 (f4ee430) into master (56475a0) will not change coverage. The diff coverage is n/a.

:exclamation: Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@           Coverage Diff           @@
##           master     #412   +/-   ##
=======================================
  Coverage   82.53%   82.53%           
=======================================
  Files          49       49           
  Lines       11684    11684           
  Branches     2185     2185           
=======================================
  Hits         9643     9643           
  Misses       2041     2041           

Impacted Files	Coverage Δ
src/gmpy2_mpz_pack.c	98.30% <ø> (ø)

:mega: We’re building smart automated test selection to slash your CI/CD build times. Learn more

[casevh]

Thanks.

Case