Issue #1 - add new pure CQL library RxSig for parsing free text SIGs, translated from a Java version

[duncand]

The initial commit, from 2018 Feb 28, just includes the new CQL library itself under pages/cql; related files under pages/elm and such will follow.

[duncand]

This pull request is now fundamentally complete as far as providing a CQL library that encodes SIG parsing, specifically a translation of the RxSig Java library by U of U, and is available in the IG with some documentation.

The library resource has a few spots marked TODO and otherwise needs the review of a more savvy person so that the right metadata is in there. The file was created by taking an existing library resource in the same folder and chopping or modifying parts as appropriate, but I didn't yet know how to finish it up.

If further documentation is required, such as examples of use, please indicate where it should go and what form it should take, with an example.

Note that this version of the RxSig.cql, while changing some things from the Java version to be more idiomatic for CQL, notably still just provides 1:1 correspondence with the parsed outputs of the Java version, such as separate result tuple values for "high" and "low" doses; a further enhancement that can and should be made is adding more result attributes that combines existing result attributes into more complex types like Interval or Quantity to make it more idiomatic for CQL.

[duncand]

Whomever has the privileges, please evaluate this merge request and accept the new library. This request has been waiting for 5 months now. Thank you.

[duncand]

Thank you for merging this pull request. Feel free to tag me if someone wants further enhancements to the RxSig library.