UTF8 support functions.

This is a small library for some utf8 support functions.

Written to be C ABI compatible.

Current functionality:

• octet_type_count Get the byte count of the utf8 octet type byte.
• get_octet_type Get the octet type of a given u8 byte.
• utf8_verify_code_point Verify a given code point is valid unicode.
• utf8_verify_str Verify a given u8 array is valid utf8 unicode.
• code_point_verify_str Verify a given u32 code point array is valid unicode.
• octet_type_from_code_point Get the octet type of a u32 code point.
• utf8_next - Get the next unicode code point from a given string.
• utf8_write - Write a given unicode code point to a given buffer.
• utf8_write_code_point - Write a given u32 unicode code point to a given buffer.
• utf8_len - Get the length of the utf-8 encoded string.
• code_point_to_utf8_len Get the utf8 byte length of an array of u32 code points.