Support of byUTF for ubyte[] argument

[vporton]

For the reasons outlined in the discussion of that pull request, we concluded that we need to be able to call byUTF on the argument of type ubyte[]. This PR implements exactly that.

I remind that this is necessary:

1. to support converting a chunk extracted from a file;
2. to eliminate the need to validate a string of chars two times: when it is created and when converted by byUTF (this simplifies programming and improves efficiency).

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[lesderid]

What happens for a range of ubytes that aren't valid UTF-8? Is this covered by a test?

[atilaneves]

I read the discussion on the other PR and AIUI it called for something that took ubyte[] and lazily produced validaded char[]. This doesn't seem to be it. Could you please explain what you're trying to accomplish? Thanks.

[dukc]

I read the discussion on the other PR and AIUI it called for something that took ubyte[] and lazily produced validaded char[]. This doesn't seem to be it. Could you please explain what you're trying to accomplish? Thanks.

The added unittest explains it: assert((cast(ubyte[]) [0x68, 0x65, 0x6c, 0x6c, 0xC3, 0xB6]).byUTF!char().equal(['h', 'e', 'l', 'l', 0xC3, 0xB6]));

You pass in a range of ubyte and get a range of char. Handy, as no separate step to deal with autodecoding is needed.

[dukc]

Perhaps this should also accept ushort (assumed to be UTF-16) and uint (UTF-32)?

Of course, this can be implemented later on just as well.

[RazvanN7]

ping @vporton