Add support for godep to pin project dependencies

`godep` appears to be solid choice for pinning Go project dependencies.
This pull request contains a `Godeps` file with SHAs of dependency
revisions. Tests were run at the specified SHAs before freezing.
Merge pull request #30 from OpenTreeMap/hmc/godep-clean

Add support for godep to pin project dependencies.
Add a CHANGELOG.
Remove Godep binary from output bin directory

During the build process, the Godep binary was sneaking into the bin
directory, which gets rolled up into a tarball for releases.
Merge pull request #33 from OpenTreeMap/hmc/rm-godep-bin

Remove Godep binary from output bin directory.