add metastore, switching sequence to use it

metastore is for storing metadata. This will be used later when moving
to distributed master mode.
adding etcd storage support for cluster meta data. Currently just
sequence. More to come...
adjust logging
remove a comment
remove unused parameter pulse
support for collections!
adjust function name
add option to split large files into parts and then upload
fix duplicated file id list entries when uploading large file
refactor api: lookup file id
formatting
fix filename not set error
added download command to download file by fileid
version 0.45!
comment out etcd support due to its os specific system calls
avoid nil cases when error
refactoring, start to use gorilla/mux
refactoring to separate master and volume server, so that these servers
can be embedded into other applications
switch to glog debugging
use glog