cantool/generate: handle mux bool types correctly + skip overflow values

[d4l3k]

This PR does two things:

1. Handles mux bool types correctly (true/false instead of 0)
2. Skips values that will overflow the type of the constant to still allow generating code with bad dbc files

Fixes #39.

[codecov-commenter]

Codecov Report

Merging #52 (cef29e3) into master (436134b) will decrease coverage by 0.40%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #52      +/-   ##
==========================================
- Coverage   55.20%   54.80%   -0.41%     
==========================================
  Files          62       62              
  Lines        3556     3582      +26     
==========================================
  Hits         1963     1963              
- Misses       1484     1510      +26     
  Partials      109      109              

Impacted Files	Coverage Δ
internal/generate/file.go	0.00% <0.00%> (ø)

[Jassob]

Hello @d4l3k, if this is still relevant please rebase on master and we'll review it again.

Otherwise we will close it in 14 days.