cext: split character encoding functions to new compilation unit
This extracts charencode.c from parsers.c, which seems big enough for me
to hesitate to add new JSON functions. Still charencode.o is linked to
parsers.so to avoid duplication of binary codes.
https://bz.mercurial-scm.org/1089
$ hg init
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b (glob)
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b (glob)
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..