tRakt 0.15.0

This is a big one, but not 1.0.0 big one I guess.
This is a consolidation release with lots of internal improvements, but for the 1.0.0 I decided to overhaul the structure of the package again, so before I completely break any kind of backwards compatiblity, I thought I'd get this one out.

Consolidation for the people

• Major refactor of the docs. Sadly, the user will only notice a little more consistency.

• Consolidate related functions into the same Rd page

• Centrally document common parameters and reuse them where needed

• Also consolidate many similar functions by factoring out the relevant bits into more flexible helper functions. In some cases those are exported as well.

• In the process, some functions where partially renamed (.show. -> .shows., .movie. -> .movies.) for consistency.

• Rename get_trakt_credentials -> trakt_credentials

• Many functions now return much flatter output, notably *people* functions. They return a list with cast and crew objects, which in turn are both flat tibbles.

Features

• Improved search function (trakt.search).
  • If the result has a year that is NA but a search score == 1000, that's probably bad and dropped.
• Added more of the automated list methods, like most anticipated, most played and most watched items.
• Added trakt.user.history for user/:id/history methods