Add support for compiled rule files.

As of yara 2.0, users can load rules from compiled binary
rule files. Users can supply compiled rules to yaraprocessor.py
by passing a single file to '--rules' and adding the '--compiled'
flag. Rule files are assumed to be uncompiled by default.

Users instantiating a processor can pass 'compiled=True' as an
keyword argument.

Error handling has been added or improved in scenarios
where compiled rules are used without the compiled flag
and uncompiled rules are used with the compiled flag.
Merge pull request #3 from MITRECND/compiled-rules

Add support for compiled rule files. Fix #2