Add 'static' data source to Nanoc core.

The original author of this data source appears to be @ddfreyne. Data source code from here:

    http://pastie.textmate.org/914015

Update `create_site` command to include a stub configuration, routing rule and compilation rule for the static data source.
cleaned up passthrough-without-extension test case
made passthrough rules be inserted in the proper order (fixes #156)
enabled utf-8 when writing to a file
Remove unused constant
Merge pull request #165 from cdlm/remove-severity

Remove SEVERITY_COLORS
Excluded files are still deleted when auto_prune is enabled

The `[:prune][:exclude]` config section is ignored when compiling with
the `auto_prune` option.

This pull request adds an extra test case and reads the exclude list
from the config file.
Merge pull request #167 from gkarekinian/fix_ignore_auto_prune_3_4

make sure excluded files are not deleted when auto_prune is enabled
Revert "fixed bug that caused progress thread not to stop"

This reverts commit ad4740a39bceaa149f43f3986ef03a306777e99c.
updated Gemfile.lock
Merge branch 'release-3.4.x' of github.com:ddfreyne/nanoc into release-3.4.x
cleaned up progress indicators
added coderay wrapper divs around highlighted pres (fixes #161)
merged release-3.4.x branch
added css checker test case
added stale checker test case
added html checker test case
Refactor CLI command setup

This could make it easier to change towards setting commands up on first invocation only.
Lazily initialize constants in commands

Needed because commands are reloaded and setup each time one of them is
run. Running several commands is actually used in tests, and has simple
use cases in normal use.
Ruby 1.8 compatible constant reinitializations