Quick, temporary fix for crash regression in 0036f0d.

mlt_image_format_size() is using height + 1.
Add Luma Key filter
Fix .yml type values to integer
Merge pull request #60 from jliljebl/lumakey

Add Luma Key filter
Generalize optimization for intra-only compression.
Revert trying to coerce XML numeric locale on Windows.

Windows does not use ISO language and country codes for locale names.
This was an attempt to avoid generating XML with locale names not
understandable on other platforms. However, this was causing more
trouble that it was worth. Often, the numeric property values would
become inconsistent (radix character) because either a properties list
had a different locale, or a property had already converted to string
under the system locale. At some point, we probably need a way to
convert Windows locale names to ISO codes.
Use Opus audio codec for VP9 WebM preset.
strict=experimental not needed for libopus acodec.
Add blank lines to dynamictext.yml for readability.
Add localtime keyword to dynamictext filter.
Add format string support to filedate and localfiledate keywords.