New join handling for plugin helpers

Resolves #419
Documentation of pluginHelpers config param
.htaccess ignore exception for assets

Resolves #646
fix my stupidity
Refactor slash helpers; Add rewire module; Fix failing test
Refactor os.platform() tests
fix #659
Merge branch 'master' into fix_659
Merge pull request #660 from szelga/fix_659

fix #659
pluginHelpers default to first joinTo file instead of last

#662
Add bower.json to watch list
pluginHelpers default by regex before filename

better backward compatibility
Merge branch 'master' of https://github.com/brunch/brunch

* 'master' of https://github.com/brunch/brunch:
  pluginHelpers default to first joinTo file instead of last
  fix #659
Refactor pluginHelpers block
Update pluginHelpers description in docs
Do os.platform() check only once.
Revert "Do os.platform() check only once."

This reverts commit a7616ed1b824f7e9b52e88db3d6a9dc21242805d.
Merge pull request #656 from brunch/topics/isWindows

Refactor os.platform() tests
Separate source map updating in sourcefile
Release 1.7.1.