Bug fixes and add boorus

[lleene]

Description

There were a couple of bugs / typos that have were fixed and optionally allows Gelbooru, e621, and rule34 booru's to be used as well.

Motivation and Context

Pybooru could not submit POST request properly and quite a few of the danbooru api calls did not work.

How Has This Been Tested?

Not formally tested but

Types of changes

• [ x ] Bug fix (non-breaking change which fixes an issue)
• [ x ] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ x ] My code follows the code style of this project (PEP-8).
• [ x ] My change requires a change to the documentation.
• [ x ] I have updated the documentation accordingly.
• [ x ] I have readed CONTRIBUTING.md.

[LuqueDaniel]

Thanks for your contribution! I missed a lot of typos... I have to do a more detailed review of your PR but I like what I've seen. Don't worry about the Appveyor error, it's caused by the pylint installation.

Due to my zero knowledge of Gelbooru or e621 the following questions arise:

Gelbooru and e621 only allow queries to the "list-like" endpoints?
Rule34 requires XML for some endpoints but JSON for others?

[lleene]

No problem. It may have been better to do PR with just the typos / bug fixes and leave the extra stuff out of it. I have been adding things as I go without being all that organized.

Rule34 and Gelbooru have very limited api unfortunately and its not well documented. The e621 api is better though and similar to danbooru with the exception that the json response is wrapped in a dictionary of lists rather than a flat list.

[ghost]

Why hasnt this been merged ?

[ghost]

Gelbootu doesnt work with certain methods. Post_images return https://gelbooru.com/posts.json?tags=md5%3A3c73f483348f9924b4b5067fbe4c0e01 instead of the poper api call format /index.php?page=dapi&s=post&q=index