[#93] Add manifest import paths as a variable

[planktonic]

Instead of a variable in the manifest file to set the import path for bitstyles sass files (to allow different paths when compiling in the bitstyles repo or when it’s installed in your local project), this PR instructs users of the library to add the bitstyles location to the path variable passed to the sass compiler (whether rails or gulp), as described in #93.

• Updated the readme to provide instructions how to install and include the sass in gulp & rails projects when using npm or bower to install the library.
• Updated references to the version number of bitstyles as the advice here will not work with other releases.

Assumes #96 #94 are merged with no functional differences to their current state.
Fixes #93
Fixes #62

[sonniesedge]

👍