add some more char and string operations to the semantics

character <-> integer conversions, character comparisons, and string length

no proofs updated yet
add char/string ops to type system, and get semantics/proofs building
get metatheory building
get inferencer working
update compiler with new operations

proofs not updated
start updating compiler proofs
get compiler proofs building
add Chr to initial program, get initCompEnvTheory building

forgot the tags in conLang need to be in the right order
fix op_apply
add some missed support for :char in ml_translatorLib
translation of char operations
remove old translaton of chars from std_prelude

There is a theorem about CHR on n MOD 256 whose functionality I have not
duplicated in the new setup. I'm not sure if it is necessary to do so...
Indeed, it may be good to look through all that is removed in this
commit and make sure it has been adequately replaced in the previous
commits.
update ml_repl_moduleScript.sml for CakeML chars
update bootstrapProofScript.sml for chars
Merge remote-tracking branch 'origin/char' into mlstring

Conflicts:
	translator/ml_translatorLib.sml
	translator/ml_translatorScript.sml