Fixing and enhancing text normalization funcitons

[bact]

• Fix: Remove repetitive tone marks - this will partially close Text normalization not working in some cases #384 and Add a more advanced normalize function #374
• Add: Remove zero-width characters - this will close Add a function to remove zero-width characters #373
• Add: Remove duplicate spaces - this will close Add a more advanced normalize function #374
• Add: Remove dangling non-base chars at the beginning of text

[pep8speaks]

Hello @bact! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2020-05-08 08:32:37 UTC

[coveralls]

Coverage increased (+0.08%) to 90.787% when pulling 0be2ea6 on feature-normalize into d1475c2 on dev.

[wannaphong]

I add docs. It's OK. 👍