Add option to use urandom for key material

Fixes #19
Add unmap option to command line tool

Fixes #17
man - Mention that mapping name should not contain spaces

Fixes #25
tcplay_api.h - Pull in stddef.h for size_t

Fixes #26
Handle TrueCrypt's nonsensical 64-byte passphrase limit

 * Document it in the man page.

 * Future API overhaul will contain a similar fix for API.

 * Avoid future strcpy problems by using strncpy.

Fixes #24
sprinkle some const as appropriate, add include guard
misc fixup
add API func to get volume info
extend API further
change build system to cmake (at least temporarily)
add missing library symbols
bump version
Duplicate cipher chains before populating with keys, etc

 * If this is not done, hidden volume protection doesn't work
   as the keys stored in the cipher chain match those of the
   hidden volume instead of the outer volume.

 * While on it, change the IV gen to plain64 instead of plain,
   which is what TrueCrypt does nowadays.

Fixes #28
Makefile cleanup, CHANGELOG update
tcplay.3 - Update for new features
Update README with cmake, etc stuff
tcplay.8 - Add info about plausible deniability
Add unmap option to getopt
print prompts irrespective of whether it's a TTY or not
in teardown, only remove dm mappings that exist