Fix freeze when reading corrupt XLSX files

[PLPeeters]

I had a case where a corrupt XLSX file caused pyexcel to hang forever when reading with iget_records.

This PR contains:

• A fix for the above
• General improvements to the regular expressions
• A migration of the tests to pytest

Ironically, my corrupt XLSX file is read perfectly fine after the changes.

With your PR, here is a check list:

• Has test cases written?
• Has all code lines tested?
• Has make format been run?
• Please update CHANGELOG.yml(not CHANGELOG.rst)
• Has fair amount of documentation if your change is complex
• Agree on NEW BSD License for your contribution

[PLPeeters]

@chfw Any chance you could take a look at this?

[chfw]

@PLPeeters , do you still need this one? I am sorry to respond late.

[PLPeeters]

@chfw No worries, glad to see you're still here :) Still need it yes, I'll rebase on dev.

[PLPeeters]

@chfw All done, but I do see the autocommit after my other PR re-overwrote the testing command to use nose instead of pytest. Tried to look into it but I'm failing to understand what generates that, so that one is for you :p