Merge pull request #62 from sappo/master

Problem: documentation has been updated in generate file.
Problem: According to gsl docs, 'include' is deprecated.
Solution: Use the 'gsl from' directive instead.
Fixed "use" dependencies in cmake target. No version checking.
Merge pull request #63 from jemc/master

Problem: According to gsl docs, 'include' is deprecated.
Merge pull request #65 from mditzel/master

Issue #64: Fixed "use" dependencies in cmake target.
Update .pc file generation with version information.
Generalize use project dependency detection, apply ordered detection, remove package_dependency as redundant.
Merge pull request #66 from pmienk/master

Removal of `package_dependency`, rationalization with `use`
Problem: No model to represent the api of a class
Solution: Add zproject_class_api.gsl
Merge with origin/master
Merge pull request #67 from jemc/master

Problem: No model to represent the api of a class
Problem: no license / contribution policy in README

Solution: added these.
Rebuilt README.md
Merge pull request #68 from hintjens/master

Problem: no license / contribution policy in README
Problem: Great article about the origin of zproject is not linked
Solution: Use the summary of hintens blog #79 and link to it for anyone
who likes a little background about zproject.