integers
(https://github.com/ruby/strscan/pull/89)

This commit adds `scan_byte` and `peek_byte`. `scan_byte` will scan the
current byte, return it as an integer, and advance the cursor.
`peek_byte` will return the current byte as an integer without advancing
the cursor.

Currently `StringScanner#get_byte` returns a string, but I want to get
the current byte without allocating a string. I think this will help
with writing high performance lexers.

---------

https://github.com/ruby/strscan/commit/873aba2e5d



Co-authored-by: Sutou Kouhei <kou@clear-code.com>