change Metrics::Archive property save_term to rotate
add testcase for rrdtool datastore class

- this class is administration and datasave to rrdtool role
change Metrics::Collection#each interface

- delete key, for metrics instance get more simply
add rrdfile create method
modified Metrics::Archive.step save value for raw date value

for fit rrd-ffi api
archive step use for raw argument

- change the Archive::Builder step hold raw date value
refacter rrd dataset type conver

- delegate collecter object extender
change module load order
setup ttdtool for travisci
fix typo...
change apt-get option and permission.
travis ci install rrdtool package changed dev package
value object create lazy
refactor collector decorate rrdtool.

- delegate properties decorate func to CollectorExtender
fix datasource name miss
move create metrics code helper to specfile.
add collection class empty? method
add Metrics class clear! method
rename Collector value method to collect
rename Collector#collect_terms method to terms