initial commit

Adding `exportmaps` and `log-region`, having fixed a typo and added
attribution as a second-line comment.  First (broken) attempt at
`exportlegends`.  `log-region` returns a nil value (for 'site') if a
world is loaded in adventure or legends mode.
add readme entries

adds readme info for `log-region` and `exportmaps`, which work.
`exportlegends` is broken and thus undocumented.
fixes log-region

stuck in an extra test that `site ~= nil` before writing; which catches
the error and also confines the script to fort mode - fortunate since
the output only make sense for fort mode.
finished exportlegends

Instead of trying to add stuff to the cycle, I just stuck two pairs of
lines in before the cycle starts.
Merge branch 'PeridexisErrant/log-region-and-exportlegends' of https://github.com/PeridexisErrant/dfhack into PeridexisErrant/log-region-and-exportlegends
add readme and init entries

includes new legends-mode section of the init file