Update config.yaml documentation for 'default:'

Current config.yaml documentation implies that default is optional, yet
omitting this field will cause charm proof to complain. Update doc to
describe the default option better.
Add draft relationships page.
Merge pull request #165 from kwmonroe/defaultUpdate

Update config.yaml documentation for 'default:'
First draft of all juju environment variables

To address lp bug #1227442
Reorg by api server and unit
add Juju environment variables to navigation
Merge pull request #167 from AdamIsrael/juju-environment-variables

Juju environment variables
Fix incorrect assumptions for JUJU_LOGGING_CONFIG
Fix broken link in authors-charm-writing.md

Also remove some superfluous slashes in a couple of other links.
Merge pull request #168 from AdamIsrael/fix-debug-environment-variable

Fix incorrect assumptions for JUJU_LOGGING_CONFIG
Merge pull request #169 from OddBloke/master

Fix broken link in authors-charm-writing.md
Adding stronger words around the requirements for configuration options.
Merge pull request #170 from mbruzek/master

Adding stronger words around the requirements for configuration options.
Initial refactoring of charm store submission doc with namespace focus.
Replace occurrences of user space with personal namespace
Merge pull request #171 from chuckbutler/submission_userspace_focus

Initial refactoring of charm store submission doc with namespace focus.
Merge pull request #166 from castrojo/relationships-docs

Add draft relationships page.
Fix typo; RELATION should be REPOSITORY
Merge pull request #173 from AdamIsrael/fix-typo

Fix typo; RELATION should be REPOSITORY
+1 LGTM