Version 1.2.0

This release brings a fair amount of changes.
Big thanks to @kazuho, who contributes and suggests a lot for this release.

Changes:

• LZ4 becomes a build-time option.
  With this release, libyrmcds can be built without LZ4. (#6, #9)
• Internal locks can be removed.
  By defining LIBYRMCDS_NO_INTERNAL_LOCK macro, internal locks are
  removed completely. (#10)
• yrmcds_shutdown to interrupt yrmcds_recv.
  This function can be used to interrupt a thread blocking on yrmcds_recv. (#8, #13)

Bug fixes:

• #4, #5, #7, #11, 6a478ad.