improvements to key handling

added a new 'change' command to change a Tomb's key
it replaces the same LUKS slot using luksChangeKey
new backup command to save keys on paper

Backup simply encodes a QRCode that can be print on paper and
hidden in books or so, to keep phisical backups of keys.
The QR can be simply scanned with any smartphone, saved into a file
and reused as a key.
important fix for backward compatibility to 1.2

a grave bug has been affecting 1.3 and 1.3.1 releases, which makes keys
created with those versions incompatible with other Tomb versions.
This bug is now fixed and Tomb should be able again to open old tombs.
A script to sanitize keys will be released soon.
documentation and test improvements

also renamed 'backup' command into 'engrave'
Improved swish indexing

swish-e usage for indexing of file contents is stable
last fixes and documentation for release

manual page updates and improvements to kdf argument handling
check if loop mount is possible

if not abort gracefully with an explanation
(10x to Bucciarati and sdonk)
fixed versioning and extras reorganization
fixes to gtk tray program
fix to engrave usage of qrencode
more post-hooks documentation and second argument passed with mountpoint
Detect non-partition swaps
Support encrypted swap
Support multiple swaps
Support encrypted swaps
Change default cipher specification

new default is "aes-xts-plain64:sha256"
manpage now includes note on how to tune it
fixes #102
Merge pull request #101 from hellekin/swap

Better support for multiple swap partitions, avoids warning if swap is encrypted.
correct documentation on -s option

somewhere mentioned as --size, but the option is really just -s
fixes #100
sanitized the way key filenames are set

there was some inconsistency in the way load_keys was accepting
different parameters or guessing from the tomb filename.

fixes #98
Resize now appends directly to tomb file

this avoids creating a delta file in ram, filling it eventually.
fixes #99