Major Overhaul & Upgrade

[reid-spencer]

This patch fixes many existing problems in scalastyle-sbt-plugin. Most notably it:

• Requires sbt 0.13.11
• Provides the plugin as an AutoPlugin
• Makes it possible to override the default settings
• Places the scalastyle-config.xml file in the project directory
• Does not differentiate between the downloaded config and the normal one. Download overwrites the scalastyleConfig file directly
• Test scope only modifies the output file name. The config file is the same as the compile case
• Adds a manual update task so the latest scalastyle-config.xml can be downloaded from the command line
• Cleans up the code a bit to be more readable.
• Documents usage in the README.md file.

[matthewfarwell]

This PR includes fixes for a number of different issues. Also, it changes existing functionality, or breaks backward compatibility (for instance requiring 0.13.11, overwriting the config file, changing the default location of the config file, etc.)

I can't accept the PR as it is, it is too complex and covers too many things. I would be happy to discuss each individual point, but not as a single PR.

Matthew.

[matthewfarwell]

There were a few too many changes in this PR to be accepted. The AutoPlugin changes have been taken from #52. If you want to make some of the other changes that you suggested, please raise separate PRs.