update debian build system

use pybuild, fix naming scheme to match debian standards
update .gitignore
Merge branch 'update-debian-packaging'
update debian changelog
fix tests
split graphite and influxdb sinks into separate files
move tests to a dedicated 'test' subdirectory
add file sink support

to log metrics directly to a file
(rotating files is supported)
update debian changelog to 0.6+hl~3
send data to influxdb with microseconds precision
compute_timer_stats is not a method anymore

(can be a pure static function)
extract influxdb encoding logic in dedicated classmethod
extract graphite encoding logic in dedicated classmethod
writing numstats is now optional for graphite sink
update graphite sink to remove use of stringio

(to make it more similar to influxdb sink)
reuse GraphiteSink.encode method for the file sink

so data will be dumped in the graphite format
don't write statsd.numStats value when using the file sink
allow proxy key customization
change maxbytes default value to 4 Mo
update debian changelog to version 0.6+hl~4