new signature for vcs provider
fix annotations
restore compatibility with old providers
store parameterized metrics in provider
finally rename "value" to "valueS"
sample implementation of incrementally behaving provider
added stub for manager
settings for first incrementally calculated metric
+descriptor
+more on descriptor
rename + separate package for incremental providers
correct Deque logic in provider
test for sample incremental provider
Merge remote-tracking branch 'origin/incremental' into incremental
Provider instances are not only supposed to be created for each project now, but also for each set of parameters. Makes provider implementations way simpler with O(1) memory overhead.
fix test and compilation
further signature simplification
separate method for per-provider cache clearing logic + get rid of push()
keeping cache size in numberofcommits provider ever equal to 1.

Some metrics, like number of affecting commits, require just one commit in provider cache for proper incremental calculation. Others (like change frequency or google score) do require potentially enormous cache if it consists of commits only. Alternatively, some other data might be stored instead of metric values itself.
 Let this remain a provider-specific choice as now we are forced to choose low memory consumption over performance.
added more stubs and bean manager