Merge pull request #726 from cgay/reader

Revert "Remove commented-out code to lex conditional compilation directives."
Merge pull request #727 from cgay/reader

[reader] Don't use the same init keyword for multiple slots in the same class.
[make-dylan-app] Add matching 'end library foo' etc.  Formatting adjustments.
Merge pull request #728 from cgay/make-dylan-app

[make-dylan-app] Add matching 'end library foo' etc.  Formatting adjustments.
[cbe] Combine methods by using if rather than singleton dispatch.
Merge pull request #731 from waywardmonkeys/remove-some-singleton-dispatch

[cbe] Combine methods by using if rather than singleton dispatch.
[doc] Fix typo in compiler-internals.rst
[doc,library] Document parser expansions as an Open Dylan extension.

This extension was originally created at Harlequin by Andrew Armstrong,
Keith Playford and Jonathan Bachrach.
[doc,library] Document macro system extensions.

As indicated in the text, the bulk of this text is from the
D-expressions paper.
Merge pull request #733 from waywardmonkeys/macro-extensions-docs

[doc,library] Document macro system extensions.
[doc] Fix formatting, typos, bugs in compiler-internals.rst.
Merge pull request #734 from cgay/docs

[doc] Fix formatting, typos, bugs in compiler-internals.rst.
[doc] grammar fixes for compiler-internals.rst
Merge pull request #735 from cgay/docs

[doc] grammar fixes for compiler-internals.rst
[dfmc] Fix grammar in a comment.
[doc] Fix typo and whitespace in macro-system-extensions.rst
Merge pull request #736 from cgay/docs

Docs
[dfmc-optimization] contol -> control (typo)
[hackers-guide] Document more about dispatch coloring.
[dylan] Add sealed member?(<byte-character>, <byte-string>) as optimization.