Special attributes do not correctly handle ">" within strings

For example, from https://www.sweetscape.com/010editor/repository/files/EXE.bt:
```
WORD IMAGE_FILE_LARGE_ADDRESS_AWARE:1 2gb addresses">;
```

The > sign inside of the string causes a parsing error:

```
Traceback (most recent call last):
File "", line 1, in
File "/home/james/__ws__/dev/pfp/pfp/__init__.py", line 91, in parse
printf=printf,
File "/home/james/__ws__/dev/pfp/pfp/interp.py", line 733, in parse
self._ast = self._parse_string(template, predefines)
File "/home/james/__ws__/dev/pfp/pfp/interp.py", line 878, in _parse_string
keep_scopes=predefines,
File "/home/james/__ws__/dev/pfp/venv3/lib/python3.6/site-packages/py010parser/__init__.py", line 137, in parse_string
keep_scopes = keep_scopes
File "/home/james/__ws__/dev/pfp/venv3/lib/python3.6/site-packages/py010parser/c_parser.py", line 178, in parse
debug=debuglevel)
File "/home/james/__ws__/dev/pfp/venv3/lib/python3.6/site-packages/py010parser/ply/yacc.py", line 265, in parse
return self.parseopt_notrack(input,lexer,debug,tracking,tokenfunc)
File "/home/james/__ws__/dev/pfp/venv3/lib/python3.6/site-packages/py010parser/ply/yacc.py", line 1047, in parseopt_notrack
tok = self.errorfunc(errtoken)
File "/home/james/__ws__/dev/pfp/venv3/lib/python3.6/site-packages/py010parser/c_parser.py", line 1952, in p_error
column=self.clex.find_tok_column(p)))
File "/home/james/__ws__/dev/pfp/venv3/lib/python3.6/site-packages/py010parser/plyparser.py", line 54, in _parse_error
raise ParseError("%s: %s" % (coord, msg))
py010parser.plyparser.ParseError: tests/templates/EXE.bt:163:77: before: 2
```

Reproduce the failure with tests/templates/EXE.bt and inspect the parsing path shown in pfp/interp.py and py010parser/c_parser.py. Confirm that the greater-than sign inside the quoted special attribute is handled as string content, then verify that the template parses without the reported error.

Written by the indexing model from the issue text.