Merge pull request #338 from dangra/scheme-s3

add s3 scheme as input stream
doc: Add a comment about ddfs chunk command.
doc: Add a note about the two different branches.
bump version to 0.5.1.
Merge pull request #491 from pooya/0.5.1

0.5.1
Merge branch 'develop'

Bumping version to 0.5.1
DDFS master node keeps track of blob sizes during garbage collection.
GC peers sends diskinfo to master on startup.
Average disk usage, over- and under-utilized nodes are now computed in ddfs_gc_main:start_gc_phase
NodeStats is updated and log message generated for every diskinfo message.
Optimization by storing the length of NodeStats in a variable.
Combined underused_nodes and overused_nodes into one function.
Added updates of Nodestats on gc_done messages.
Changed find_unstable_nodes to use pattern matching on input.
Added estimate_rr_blobs/1 to estimate effects of rr_blobs.
Renamed variable.
Added function for marking blobs for rebalancing.
Minor style changes to estimate_rr_blobs.
Enabled replication of blobs selected for rebalancing.
Change do_choose_write_nodes to choose the most under-utilized nodes.