fixes #162: Allow import of a context-spec into another.
Merge branch 'master' into enh-manage-imports
Put mergeSpecs() and mergeAll() in a separate module.
Add short description of `$imports` keyword.
Review description of `$imports` keyword.
Track cycles by names.
Allow nested imports with circular imports detection.
Update docs to reflect the last updates:
* Track cycles by names.
* Allow nested imports with circular imports detection.
Review as per @briancavalier comments.
Fix typo and rename arguments and variables for better understanding.
Merge pull request #164 from ouadi/enh-manage-imports

fixes #162: Allow import of a context-spec into another.