Add rav1e_config_parse_bool

[lu-zero]

Act as helper to set boolean values.

Fixes: https://github.com/xiph/rav1e/issues/2155

[dwbuiten]

I feel like using parse_int with 0 and 1 feels more like idiomatic C, but also I don't have a stong opinion on it.

@tdaede any opinion from you?

[lu-zero]

If you tested it I'd go and merge it

[lu-zero]

Poke.

[lu-zero]

I'd land it for 0.5.

[coveralls]

Coverage increased (+0.004%) to 83.525% when pulling 9dcd9726c2b903c4e203fb3cf9a82bbda91576a4 on rust-av:capi-parse_bool into 7970d35ebb1424358b837c6e19b0cecf3cc6f8df on xiph:master.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (e006c0e) 88.24% compared to head (5a8deb9) 88.24%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2157   +/-   ##
=======================================
  Coverage   88.24%   88.24%           
=======================================
  Files          88       88           
  Lines       28210    28210           
=======================================
  Hits        24893    24893           
  Misses       3317     3317           

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