Allow builds via node-gyp.

node-gyp disables C++ exeptions, presumably for performance reasons, so we
have to enable those ourselves. I'm unsure why but catching Exiv2::AnyError
is no longer sufficient to handle invalid file paths. Switching to its
parent class std::exception resolved the problem and seems reasonable since
we're not using AnyError's functionality.
Updates to the README.

Split out the installation instructions to make the platform specifics clearer.
Fixed a bug in the sample code.
Reverting the travis stuff

It's not that useful since it won't build our extension.
Make sure gcc enabled exceptions.
Merge pull request #15 from drewish/node-gyp

Add node-gyp support.
Starting to add support for setting IPTC and XMP tags.
Bumping version number for 0.3.0 release.
Remove the Travis-CI stuff.