Look for invalid characters not part of a regex

[igponce]

The search must be either a string part of an ethereum address or a regular expression.

If we have some characters that can be part of a regular expression like backslash(), dot(.), {}, comma(,), etc... Then we compile the regex and use it. Otherwise we throw an error because the string cannot match an ethereum address.

It is still possible to search for regexes that cannot match an Ethereum address like:

[fe]+o , [fe]o, feo[], or feo\n

But at least we reduce the possibility of giving a simple string like 'feo' that cannot be part of an Ethereum address.

Closes vanieth#3