Add BoolFromInt adapter

[jonasbb]

Closes #456

[codecov]

Codecov Report

Merging #462 (82bd5b8) into master (b3d4156) will decrease coverage by 0.50%.
The diff coverage is 49.39%.

@@            Coverage Diff             @@
##           master     #462      +/-   ##
==========================================
- Coverage   71.87%   71.37%   -0.51%     
==========================================
  Files          54       54              
  Lines        3634     3717      +83     
==========================================
+ Hits         2612     2653      +41     
- Misses       1022     1064      +42     

Impacted Files	Coverage Δ
serde_with/src/lib.rs	75.00% <ø> (ø)
serde_with/src/de/impls.rs	64.42% <32.25%> (-8.46%)	⬇️
serde_with/src/ser/impls.rs	93.85% <100.00%> (+0.10%)	⬆️
serde_with/tests/serde_as/lib.rs	100.00% <100.00%> (ø)

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[jonasbb]

bors r+

[bors]

Build succeeded:

• Rustsec Audit
• Tests result