Improve sphinx documentation

[skirpichev]

• 30ab80d Add docs/misc.rst (Miscellaneous Functions)
• a7a4971 Add docs/generic.rst (Generic Functions)
• 97da2b1 Add docs/exceptions.rst (Exceptions)
• 366104f Rename docs/overview.rst -> docs/tutorial.rst (Tutorial)
• 153e696 New docs/overview.rst page
• c2152ec Rename chapters for integers/rationals
• a94503a Move down "The xmpz type" section
• a3c536e Expand docs/tutorial.rst

[codecov-commenter]

Codecov Report

Merging #455 (a3c536e) into master (e002e2c) will not change coverage. The diff coverage is n/a.

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

@@           Coverage Diff           @@
##           master     #455   +/-   ##
=======================================
  Coverage   84.96%   84.96%           
=======================================
  Files          49       49           
  Lines       11736    11736           
  Branches     2204     2204           
=======================================
  Hits         9972     9972           
  Misses       1764     1764           

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[casevh]

Thanks.