Implement operator + (__add__)
Implement operator * (__mul__)
Simplify parser.at_least() implementation using new operator +
As a side effect, the code is now syntactically correct in Python 2
Can't raise a string
Use dedicated str methods' arguments instead of creating a slice
Simplify column number calculation by removing special-casing
(since str.[r]find returns -1 when the substring is not found)
Don't fail while trying to report an error if stream is not a string
Remove 'parse error:' from error message since it's going to be displayed as the class name anyway
Simplify Parser.many() and Parser.times() code
Merge pull request #4 from bugaevc/operators

Implement additional operators
improve parse errors by tracking the furthest failure

this is the approach already taken in Parsimmon
add seq and reimplement then, skip, and add
Merge pull request #3 from bugaevc/error_reporting

Error reporting fixes
more explicit oob error message and catch not-a-string earlier
docstring update