Make functions setup-LANGUAGE-environment

Make functions setup-LANGUAGE-environment
interactive and add new functions describe-LANGUAGE-support for
all LANGUAGEs supported.  Remove resisterations of input methods
which use the function encoded-kbd-select-terminal.
Change function of post-read-conversion
and pre-write-conversion of coding system in-is13194-devanagari to
in-is13194-devanagari-post-read-conversion and
in-is13194-devanagari-pre-write-conversion respectively.
Setting of syntax and category for Devanagari characters are moved
to characters.el.