Updated todo to reflect caching.

Some data from linux-2.6 and wine repositories:

linux-2.6:

Execution time 8574.73483 secs, 8539.54468 secs (99.59 %) in external commands)
Execution time 532.61431 secs, 509.50925 secs (95.66 %) in external commands)

-> time reduced to ~6%

wine:

Execution time 1538.62315 secs, 1512.65805 secs (98.31 %) in external commands)
Execution time 341.02903 secs, 331.91908 secs (97.33 %) in external commands)

-> time reduced to ~22%

And this is just one particular function that is cached.

The downside is more used diskspace, the cache for linux-2.6 for example
is 2.9 MiB at the moment.

doc/TODO.txt

 - Commandline options
 	--title "Project name"
 	--debug / --verbose
-- state saving/restoring?
-	- could save data that can not be recreated quickly (for example files/lines data)
-		- tags
-		- files_by_stamp could be cached
-	- would have to cope with cases where history is rewritten
-	- use pickle.dump() & pickle.load()
-	- where to save the state file? <repo>/.git/gitstats.dat ?
-	- also save command line settings and use them next run if not overridden?
+- save command line settings and use them next run if not overridden?
 
 [Stats]
 - General