Bump version number and label.

There have been some new APIs added, so 1.0 -> 1.1 seems appropriate.
Merge pull request #60 from atgeirr/bump-version

Bump version number and label.
Install header-only pkgconfig file to generic lib/

The previous version assumed that we had libraries, and thus always
installs the .pc file in the multi-arch library directory. However,
we now have modules which does not have a library, but whose header
files still need to be located. Since the lib/ directory is usually
in the pkgconfig search path, it is natural to put them there.
Merge pull request #61 from bska/061_cmake

Synchronise build system with opm-core