Add wishlisted methods to Pithub::Repos.

[jjatria]

This patch adds two methods to Pithub::Repos: ->issues and ->pull_requests. These act as shortcuts to access a Pithub::Issues and Pithub::PullRequests inheriting the parameters from the parent repo.

This makes it easier to use Pithub in the way requested in #194 and #196.

This PR brought to you by the CPAN pull request challenge.

[coveralls]

Coverage increased (+0.003%) to 99.075% when pulling 7a01e14 on jjatria:wishlist into 6ec66c3 on plu:master.

[coveralls]

Coverage increased (+0.004%) to 99.017% when pulling da68228 on jjatria:wishlist into ad4c3ba on plu:master.

[coveralls]

Coverage increased (+0.004%) to 99.017% when pulling da68228 on jjatria:wishlist into ad4c3ba on plu:master.

[oalders]

I think if you rebase using the latest changes from master we should get a fully passing build on this branch.

[oalders]

LGTM. @plu?

[plu]

Looks great! Thanks for adding tests 👍