Created a 'br-shims' library that contains references to all the other
shim libraries we ship in brjs by default, and which users can override
and re-define within their own applications if they would prefer to use
a different set of shims, or use no shims at all. The library previously
called 'caplin-ie8-shim' was also renamed to 'br-ie8-shim' as part of
this work, and we switched to having shims export null rather than the
empty object literal, since this doesn't require the use of quotes.
Finally, it was necesarry to temporarilly rename the 'package.json' file
within 'es5-shim' as our interim support for Node.js libraries was
causing us to attempt to redefine 'null', which caused a JavaScript
error.