Full valid escape sequences

Cover all valid escape sequences including hexadecimal character codes.
Test parsing of valid escape sequences

Remove special casing of `\x` and let levels above parser, such as the
annotator deal with telling the user that they are missing hexadecimal
digits or braces after `\x`.
Merge branch 'master' into feature/15/char-escapes
Add test case for #14

Closes #14

Test that escaping sigil terminators prevents sigil termination to
ensure that #14 is fixed by implementing all valid escape sequences for
 #15.
Update change logs
Land #17, Full valid escape sequences

Fixes #14
Closes #15