lib: tutf8e: A tiny UTF-8 encoder for C

[nigels-com]

For encoding UTF8 from iso-8859 and windows-125* 8-bit character encodings.
Input plugin support to follow in subsequent PRs, to be finalised.

$ ls -lah library/libtutf8e.a 
-rw-rw-r-- 1 nigels nigels 23K Nov  2 09:07 library/libtutf8e.a

Based on previous work with iconv: #1180
A portion of the proof-of-concept implementation: #1668

[edsiper]

what do you think about having the option name FLB_UTF8_ENCODER ?

[nigels-com]

Yes, that makes sense.

[edsiper]

FLB_UTF8_ENCODER

[edsiper]

thanks!