Factor modules into smaller files; rename polyfill to `HTMLImports.js`
change file case
Delete unused workbench files.
importer now uses Observer singleton.
slight renaming.
re-add flags support.
Update sourceURL moniker to not be Polymer specific
make tests pass on IE10 (IE10 does not support dynamic elements in imports).
avoid processing when using native HTMLImports
add modules to help manage code execution; lim native build; maor comments.
refine comments.