Minor formatting change on changelog.
Declare alex and happy as build-tools.

Closes #986.
Fixed typo in changelog: pandoc-citations -> pandoc-citeproc.
make_osx_package.sh:  Add dylibs needed for text-icu.
Depend on pandoc-types 1.12.1.
Allow `--metadata` to be repeated for the same key to form a list.

This also has the effect that `--bibliography` can be repeated,
as before.
More informative error when a filter is not found in path.

No more "resource vanished (broken pipe)"!
Fixed reference slides.

The Div container around references messed up the procedure
for carving a document into slides.  So we now remove the surrounding
Div in prepSlides.
DOCX writer: Add  missing settings.xml to the zip container.

Closes #990.
LaTeX writer: Don't print biblio if --natbib or --biblatex option used.
Markdown reader: small code improvement.
Handle Boolean values in `--metadata`.

Note that anything not parseable as a YAML boolean or string
is treated as a literal string.

Note that you can still get a string value with "yes" or any
of the strings interpretable as booleans:

    -M boolvalue=yes -M stringvalue='"yes"'
Documented `--metadata` change.
Added small explanation of difference btw `-M` and `-V`.
Added something on unicode_collation to INSTALL.
Don't use unicode_collation in building OSX package.

It adds something like 50MB of dependencies to the package.
Version bump to 1.12.0.1.
Updated changelog.
make_osx_package:  small code cleanup.
Added --force in make-windows-installer.bat.