Check List of methods for methods from `Vec` which need to be added.

[rustonaut]

Go through all "new" methods and add proxies where necessary and possible. (Note that some methods are from slice deref, so they are automatically exposed).

• [x] splice
• [x] chunk_exact, chunk_exact_mut,
• [x] rchunks, rchunks_mut,
• [x] rchunk_exact, rchunk_exact_mut,
• [x] rsplit, rsplit_mut,
• [x] sort_unstable, sort_unstable_by, sort_unstable_by_key,
• [x] rotate_left, rotate_right,
• [x] swap_with_slice,
• [x] align_to, align_to_mut,
• [x] is_ascii, eq_ignore_ascii_case,
• [x] make_ascii_uppercase, make_ascii_lowercase
• [x] to_ascii_uppercase, to_ascii_lowercase
• [x] try from Box<[T]>
• [x] try from BinaryHead<[T]>
• [x] try from String
• [x] try from VecDequeue
• [x] into VecDequeue
• [x] into Box<[T]>
• [x] into Rc<[T]>
• [x] into Arc<[T]>
• [x] try from &str
• [x] try from CString
• [x] try from &[T]
• [x] try from &mut [T]