(closes #342) add reference guide

[arporter]

Adds a reference guide at https://fparser-ref.readthedocs.io/en/342_reference_guide (I'll remove the version pointing at this branch once it makes it onto master).

[codecov[bot]]

Codecov Report

Base: 91.62% // Head: 91.61% // Decreases project coverage by -0.01% :warning:

Coverage data is based on head (3fad56a) compared to base (3e5896e). Patch coverage: 100.00% of modified lines in pull request are covered.

:exclamation: Current head 3fad56a differs from pull request most recent head 8749796. Consider uploading reports for the commit 8749796 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #377      +/-   ##
==========================================
- Coverage   91.62%   91.61%   -0.01%     
==========================================
  Files          37       37              
  Lines       13283    13279       -4     
==========================================
- Hits        12170    12166       -4     
  Misses       1113     1113              

Impacted Files	Coverage Δ
src/fparser/common/base_classes.py	68.33% <ø> (ø)
src/fparser/common/readfortran.py	94.80% <ø> (+0.02%)	:arrow_up:
src/fparser/common/utils.py	75.23% <ø> (ø)
src/fparser/one/block_statements.py	78.53% <ø> (ø)
src/fparser/one/statements.py	85.87% <ø> (ø)
src/fparser/one/typedecl_statements.py	83.20% <ø> (ø)
src/fparser/two/Fortran2003.py	94.41% <ø> (+<0.01%)	:arrow_up:
src/fparser/two/pattern_tools.py	92.40% <ø> (ø)
src/fparser/two/utils.py	95.59% <ø> (ø)
src/fparser/two/Fortran2008.py	99.31% <100.00%> (+<0.01%)	:arrow_up:
... and 5 more

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[arporter]

Ready for review from either @rupertford or @sergisiso. I've basically replicated what's done for PSyclone.

[arporter]

Ready for another look now.

[arporter]

The GHA CI was still attempting to use Python 3.6 so I've replaced that with 3.7 and also moved 3.10 on to 3.11.

Ready for another look now.