Tidy up
Link to libgsf
Using PKG_CHECK_MODULES in configure.ac (pkg-config macro)
Updated configuration script
Using low-level md5 function is faster (480,000 key/sec vs. 430,000)
Fix Makefile
Must not use OpenSSL md5.h header if we're using Solar functions

There should also be conflict with the library symbols, although
everything appears to work fine.
Handle BoundSheet8 record properly
Keystream was not being initialized correctly
Add documentation of "--decrypt"
Add checks for <signal.h>