This commit changes the caching mechanism to use the timestamp of
all included templates instead of hashing the contents of the
root template.
The primary downside is that every build now has to parse, transform,
and resolve the input templates instead of just reading and hashing
the data--I didn't measure how much more expensive this is, but it
seems unavoidable if we need information about child templates.
Maybe a hacky regex-based approach could work as an alternative to
a complete parse.
On the bright side, this approach rebuilds parent templates correctly
when a child template has changed, and doesn't require garbage collection
for old compiled template files.
01ba06707b