gzip reader and writer
add performance test
switch to hadoop Gzip (faster) and fix merge bug
incorporate all changes suggested by pawel
add param to specify reader/writer
add Compression util method
NPE fix
remove unused imports
mock gzip file input/output stream for tests
changes Pawel suggested
enhance comment for file reader writer interface
Merge pull request #33 from lefthandmagic/gzip

Gzip writer/reader