Fix fr_utf8_strchar() and tests

allowed characters shouldn't be escaped in the test.

the function returns const

it checks for fr_utf8_char() of str, not char the second time
around
* use the same json token parsing function everywhere
* cleanup now un-used functions in jsonc_missing
* minor function naming cleanup in mod.c
* add missing prototype to mod.h
Merge pull request #827 from leprechau/tokener-cleanup

minor cleanups