Resolves #1036

Summary:

• When trim_block is enabled and a block ends with +%} or +#}, the behavior will be ignored.
  • Note: does not apply to raw start tags (i.e. {% raw +%} will raise an error) because they don't process the inner text
  • +%} is still allowed when trim_block is disabled but exhibits NOP behavior
  • So following the example from the original issue, when trim_block is enabled:

{% if something %}X{% endif +%}
more things

results in

X
more things

Tests:

• Added tests to test_lexnparse.py
  • Specifically added a class for testing trim called TestTrimBlocks
  • Tests majority of the same cases as TrimLstripBlocks

Files affected:

• lexer.py
• test_lexnparse.py