Fix/Update Charm Author Formatting

[Antonio Rosales]

In the import of charm author docs from the "old" format it seems some formatting did not get translated over correct. One example is the code sections in https://juju.ubuntu.com/docs/authors-charm-writing.html. Some code sections have abundant spacing and others have very little.

[Kapil Thangavelu (hazmat)]

The problem is the css rule for the pre sections

white-space: pre-line