Implement const (compile-time) functions

[mtshiba]

Almost all of Python's standard functions are implemented in Erg, but we will re-register those of them that can also be executed at compile time as compile-time functions.

TODOs

• abs
• all
• any
• array
• ascii
• bin
• bytes
• bytesarray
• chr
• dict
• enumerate
• format
• filter
• frozenset
• hash
• int
• iter
• len
• map
• max
• min
• not
• oct
• ord
• pow
• range
• repr
• reversed
• round
• set
• slice
• sorted
• str
• sum
• zip

Str methods

• endswith
• find
• isalpha
• isascii
• isdecimal
• join
• replace
• startswith

Array methods

• __getitem__
• union
• shape
• sum
• prod
• reversed

Dict methods

• __getitem__
• keys
• values
• items
• concat
• diff
• as_record