Returning smart_ptr validity requires bool operator.
Prefer to use static_cast over Boost's bool operator.
Add release notes file.
Merge pull request #33 from dstoup/fix-compile-issues-vs2013

Fix compile issues vs2013
Merge branch 'release'

* release:
  Add release notes file.
  Prefer to use static_cast over Boost's bool operator.
  Returning smart_ptr validity requires bool operator.