stringify frames per as_string (#19)

[bpj]

See #19.

I had to give overload an anonymous sub which calls as_string on the object rather than giving it \&as_string or 'as_string' or arguments wouldn't be shown properly in the stringification. Probably because of generated accessors which don't exist yet?

I added a very basic test checking that the stringification is identical to the return value of $frame->as_string. It caught the above problem so apparently not too simple!

[bpj]

I have no idea why tests fail. They succeed locally.

[autarch]

I think you used an older version of Perl::Tidy locally to tidy your code. You need to use the latest version from CPAN.

[bpj]

Yes perltidy was the problem, but the real problem was that perlbrew was using the wrong perl. I must have said perlbrew switch instead of perlbrew use at some point.