Improved discussion and examples

[anarthal]

Added a tutorial on UPDATEs, transactions and multi-queries
Added a tutorial on connection_pool
Added a tutorial on error handling
Added examples on INSERTs and DELETEs
Rewrote the discussion page on character sets
Added a discussion page on the templated connection class
Removed superseded examples on timeouts and multi-queries
Updated the coverage build to gcc-14 (gcc-13 was using a non-LTS release that caused problems)

Contributes to #365 and #366

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.95%. Comparing base (ef9224c) to head (cb39a2c).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #381   +/-   ##
========================================
  Coverage    98.95%   98.95%           
========================================
  Files          142      142           
  Lines         7185     7186    +1     
========================================
+ Hits          7110     7111    +1     
  Misses          75       75           

see 1 file with indirect coverage changes

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