Enhanced paths

A few breaking changes in this version, but the new features are super sweet and well worth it.

Updates:

• All module states are extended with $parent which allows submodules to read their parents state and thus the parents other submodules.
• The library is now optimized to use strings for paths instead of the api. The api is deprecated and will be removed in the next major version.
• Global is removed (breaking change) and root is introduced.
• root accepts keywords together with context.state to make path navigation simpler. Easy access to parents getters and the root module in the same instance tree.
  • root.get({ path: '$parent/getter', state: context.state }) expands to full path with parent instances
  • root.get({ path: '$root/getter', state: context.state }) expands to root module instance path
• addStore is removed (breaking change) and register is introduced.
• register takes a store name and returns a mixin that can be used instantly in the mixin property.
• To get the Vue and Vuex plugins are now accessed through functions from Vuex+ (breaking change). It was necessary to be able to patch Vuex to add $parent when inserting new states through Vue devtools.
• Works nicely mixed with normal vuex modules. By following file naming conventions they also get automatic HMR.
• Bug fix where files with -store in middle of the filename would get weird module names.