Make filter paths absolute

[RPGillespie6]

Use absolute path when deciding what to filter when using filter flags --exclude and --include

Description:

• Fix Include filter uses relative path / revisit sources/include/exclude #17
• Fix Out of source builds produce coverage for generated files #33

[codecov-io]

Codecov Report

Merging #34 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #34   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines         330    330           
=====================================
  Hits          330    330

Impacted Files	Coverage Δ
fastcov.py	100% <100%> (ø)	⬆️

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