Utilities to convert to/from utf-8, utf-16.

[fabioz]

First step to solve #134

[fabioz]

As a note, with these differences, I've done a change to just convert indexes back to utf-16 and things almost seem to work.

You can see my changes at:

fabioz/LiClipseText@1d8f88c

So, mostly I just convert the result back to utf-16 (as everything should be dealing with utf-8 internally), now, I have a strange difference in that it appears that the grammar found an intermediary match that it didn't find first, so, I'm not submitting a pull request because of that...

i.e.:
I expected my test to have the same results with chars with and without unicode chars, yet, as you can see in:
fabioz/LiClipseText@1d8f88c#diff-9b217bdbf9f5aee0083ab4831116a634R62

it's not really exactly the same (the assertEquals above is the one without unicode and the below is with unicode -- the result should be the same).

[angelozerr]

Thanks a lot @fabioz for your PR. Let me find time to study it and compare with VSCode.

[angelozerr]

@fabioz I hope I have fixed problem with UTF-16 (see #134)

I have tested #134 and #136 and it seems it works well in Windows context. Please give me feedback.

I'm using your convert methods which works well, Thanks!