Add Docker support

[PuKoren]

Dockerfile used to create a container for bloomd (running on Alpine)

Some configuration options can be set using env variables:

Name	Default value	Description
BLOOMD_PORT	8673	Port used to listen to incoming connections
BLOOMD_LOG_LEVEL	INFO	Log level
BLOOMD_DATA_DIR	/data	Folder used to store bloomd databases
BLOOMD_FLUSH_INTERVAL	300	Flush interval to write changes to disk
BLOOMD_WORKERS	2	Number of workers

Build:

docker build -t armon/bloomd:latest .

On this PR, you will encounter this error when building: https://github.com/armon/bloomd/issues/54

Run:

docker run -it --rm -p 8673:8673 armon/bloomd:latest

With shared folder:

docker run -it --rm -p 8673:8673 -v `pwd`/datafolder:/data armon/bloomd:latest

Image size: 5.71MB