Remove the import-as and import-from builtins

The new and improved (import) can handle all cases import-as and
import-from did, so drop the latter two from the language. To do this,
the import builtin had to be changed a little: if there's a single
import statement to return, return it as-is, otherwise return a list of
imports.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Add context manger / 'with' statement to tutorial
Remove unneeded line from TODO section
whitespace in doc
more TODOs
Merge branch 'master' of github.com:hylang/hy
Adding @egenhombre to AUTHORS
Merge branch 'master' into pr/125
Merge branch 'master' into pr/146
Merge branch 'master' into pr/145
Merge branch 'master' into pr/144
Introduce a context manager for compiler.returnable

Signed-off-by: Julien Danjou <julien@danjou.info>