Fix #37 (broken `t` parent fallback for empty child locales)

Dictionary compilation automatically inherits parent locale translations
to child locales. Problem was: this only works when the relevant child locale
is present in dictionary at compile-time.

So `(dict-compile {:en {:foo "bar"} :en-US {}})` works as expected, but
   `(dict-compile {:en {:foo "bar"}})` does NOT.

Simplest soln is to search for possible parent translations at runtime.
There's a performance cost, but it's reasonable.

Unit test was failing to catch this up since the :fallback-locale was
masking the problem; tests updated to make this catchable in future.
Experimental, undocumented: add `t'` fn
cljs: add skeleton ns for cljs-side Tower
cljs: get compile-time dict compiler working
cljs: add experimental `translate`, `t` fns.
Move macros to allow use with cljs 0.0-2120+ :include-macros
Ref. https://groups.google.com/forum/#!topic/clojure/mUVbtdnAvHA