Add normalized distances to `all` results
Add test for normalized distances
Merge branch 'feature/normalize-results'

This breaking new feature makes the numbers returned by `franc.all()`
more usefull by interpolating them between the most probable
language's distance, and the maximum distance.

Normalized results make it easier for developers (see GH-13) to
know how 'sure' franc is about the most probable language, for example
by checking if the difference between the primary and secondary
languages is more than `n` (where `n` could be, for example, `0.9`).

The resulting numbers are now guaranteed to be between (including) `0`
and `1` (including).
Add test for valid iso-639-3 code
Add debug statements with language names
Add option to set threshold through an ENV variable
Add custom fixtures for `gug`, `gyr`, `eve`
Fix multi-script languages with few divergent characters
Add longer fixtures when franc supports 200+ languages
Add support for languages without fixtures
Remove support for `cbs`, `prq`

Because OHCHR has the same entries for these different (?)
languages, franc cannot guarantee correct classification
of these languages.
Fix typo in `build-languages`

`en` > `an`
Update docs for new build CLI
Merge branch 'feature/add-build-cli'

This new feature makes it easy to create a version of franc with
support for just how many languages you want, be it 335, or 50.

In addition, this merge explicitly enables support for all these
languages by passing all tests on whatever threshold is provided.
Add explicit mention of maximum supported languages to `Readme.md`
Update example output in `Readme.md` for changes in 8b339ad
Update example build-process in `Readme.md`
Update changelog for 0.5.0
0.5.0