\x escape sequences not parsed

[spyoungtech]

Currently \xnn escapes are not supported.

Relevant spec:

Any character may be escaped. If the character is in the Basic Latin or Latin-1 Supplement Unicode character ranges (U+0000 through U+00FF), then it may be represented as a four-character sequence: a reverse solidus, followed by the lower case letter x, followed by two hexadecimal digits that encode the character’s code point. A reverse solidus followed by the lower case letter x must be followed by two hexadecimal digits.

Additionally, the rule that a \x must be followed by two digits is not currently enforced.