Avoid loading invalid numeric config entries

Don't try to load old style "true"/"false" config entries as integer. This
would cause an value error and crash m64py. Instead try to load the content
only when it is valid and otherwise use the m64py default value.
Fix recent_files config option automatically

The recent_files list has to be an python object serialization. This object
must be an array of strings. Python will save unicode strings and Python3
strings. Not following this rule make m64py crash either while loading the
recent_files information or when adding a new entry when a file is opened.
Validate size config values to avoid crashes
Merge pull request #23 from fayvel/config_int

Avoid loading invalid numeric config entries