Add some Rust lang functions

[juliancoleman]

JS Strings are stored as utf-16, so if I want them stored as utf-8 (rather, utf-8-like, since they will still be utf-16 when converted back), we could filter a string, keeping only values that lie within a certain codepoint range.

https://doc.rust-lang.org/std/string/struct.String.html https://doc.rust-lang.org/std/primitive.str.html

[juliancoleman]

Because JS isn't a memory-safe language (in that memory is dynamically allocated), there are a number of functions that simply can't be added unless I made a new String class, which I won't do. The biggest question is: do I want to use generators where Rust uses iterators? Also, if I find out that this whole bytes thing isn't going to work out like I planned it to, then that sucks, but at least I'd have learned something

• [ ] from_utf8
• [ ] from_utf8_unchecked
• [ ] from_utf8_lossy
• [ ] from_utf16
• [ ] from_utf16_lossy
• [ ] into_bytes
• [ ] push_str (String.prototype.concat)
• [ ] truncate
• [ ] pop
• [ ] retain
• [ ] insert
• [ ] insert_str
• [ ] len
• [ ] is_empty
• [ ] split_off
• [ ] clear
• [ ] replace_range (may not implement as String.prototype.replace exists)
• [ ] is_char_boundary
• [ ] split_at
• [ ] chars
• [ ] char_indices
• [ ] bytes
• [ ] split_whitespaces
• [ ] split_ascii_whitespaces
• [ ] lines (Already in library as splitLines; may rename to lines)
• [ ] encode_utf16 (? need to do some research on how this works)
• [ ] contains (make this blazing fast)
• [ ] find
• [ ] rfind
• [ ] rsplit
• [ ] split_terminator
• [ ] rsplit_terminator
• [ ] splitn
• [ ] rsplitn
• [ ] matches
• [ ] rmatches
• [ ] match_indices
• [ ] rmatch_indices
• [ ] trim_matches (Similar to underscore.string/trim)
• [ ] trim_start_matches (Will come much later)
• [ ] trim_end_matches (Will also come much later)
• [ ] parse
• [ ] is_ascii
• [ ] eq_ignore_ascii_case
• [ ] make_ascii_uppercase (hmm..)
• [ ] make_ascii_lowercase (...)
• [ ] replacen