Add kobachi to contributors (ja-JP locale).
Add zh-TW locale.

Traditional Chinese locale contributed by on9123.
Add et-EE locale.

Estonian locale contributed by mdr.ksk.
Use in-built test for acceptable input types.

When checking to see if the current focussed element is a valid text
input element, use the Mozilla in-built API for this instead of a
hardcoded list of types. Passing true to the API excludes password input
fields.
Remove redundant code.

aChars is always null or 16, so can never be over 150. The ternary
condition capping characters at 150 would never apply and so should be
removed.
Increase version number and set compatibility.

Increase version number to 0.6.3 in preparation for release and set
the maxVersion to 29.* (based on the beta) ahead of its release.