Increment channel reference count on mmap copy.

Fixes #360.
Increment reference count by channel offset.

o Adds new pfs_channel_addref function. mmap constructors now add a reference.
o Move deleting the channel reference to the mmap destructor.
Merge pull request #418 from btovar/graph_wq

Optionally specify time scale for work_queue_graph_log.
Increment channel reference count on mmap copy.

Fixes #360.

* ccl/pull/415/head:
  Increment reference count by channel offset.
  Increment channel reference count on mmap copy.
Initial weaver commit.
Clean up some readme files
Added weaver.html.