Shared Eyeglass Configuration

[chriseppstein]

The Eyeglass API is currently optimized for wrapping a call to sass by transforming the options for a single compile. Often there are many files to compile that share the same compilation options and the work to discover eyeglass modules can be shared across those compiles.

In Eyeglass 3.0 we should expose a new class that optimizes for compiling many stylesheets and sharing the work of module discovery and resolution. The goal would be that this instance can be long lived and used to compile multiple versions of the same files over time.