Generate Version even on `--no-build` (iwillspeak#33)

If `--no-build` is specified we currently don't generate the props file. Fix that by using `BeforeBuild instead.

Register as TFM Specific Pack File. It isn't really, but this ensures the file is always generated and evaluated for inclusion in the package.

Update README

Check off SDK support in README

Simplify External Type Resolution

Remove some of the indirection from external type resolution now that
we don't pre-walk the externs.

Update License Years

Chibi R7RS Tests (iwillspeak#11)

This PR introduces a modified version of the Chibi Scheme R7RS conformance tests to the spec/ folder. Also includes a simple SRFI-64 test library implementation.

This test suite checks for R7RS compliance, most of it is commented out
for now.

Move Writer Functions to Serefa

Move the `display` and `newline` builtins to the Serefa library. Here
we can hopefully extend them with better support for displaying external
representation and add a `write` impl too.

Fix NRE in Display `()`

When given the empty list `display` would throw due to calling
`ToString` on `null`.

Fixes iwillspeak#2