Merge `ParseError` with `Error`, convert `Parsed_set*`

[pitdicker]

It is tricky to slice up the work to convert our parsing module from returning ParseError to Error. After a couple of attempts the best way seems to be to merge the ParseError and Error types first, go over all the methods to clean them up for the new type and remove the constants next, and attach more information such as the location of an error last.

The first two commits merge ParseError and Error, and the last one goes over the Parsed_set* methods.

I have a branch to go over plenty more methods and tests, but this seems like enough to review in one PR.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.39474% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 94.05%. Comparing base (21ee9b7) to head (983d846).

:exclamation: Current head 983d846 differs from pull request most recent head 36def24. Consider uploading reports for the commit 36def24 to get more accurate results

Files	Patch %	Lines
src/error.rs	50.00%	3 Missing :warning:
src/format/parse.rs	83.33%	2 Missing :warning:
src/format/parsed.rs	98.41%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##            0.5.x    #1511      +/-   ##
==========================================
+ Coverage   93.96%   94.05%   +0.09%     
==========================================
  Files          37       37              
  Lines       16662    16972     +310     
==========================================
+ Hits        15656    15963     +307     
- Misses       1006     1009       +3     

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