Process declarations and docstrings correctly for flet+, labels+, lambda+, defun+

For now, declarations are ignored instead of ending up somewhere in
the expansion.

Docstrings should appear at the correct syntactic position in the
expansion.

Added test for docstring in defun+.
Merge pull request #5 from scymtym/wip-defun-plus

Process declarations and docstrings correctly for flet+, labels+ ...
Made defun+ etc pass through declarations.

Also added test for it.
Increased version number.

Fixes https://github.com/tpapp/let-plus/issues/6.
Added &do.
Removed &assert and &do.

Decided it was bad style to mix code purely for side effects in a let+ form.
Removed tests for &assert.
Documentation improvements for expand-{slot,entry}-forms
Merge adjacent &LABELS bindings into a single CL:LABELS form
Slightly improved support for declarations

* Declarations are separated from body

* Expansions receive declarations and handle them as appropriate

* Built-in expansions handle declarations

* Limitation: bound declarations (like CL:IGNORABLE) are not
  associated with the correct expansion