Prevent indention for lines starting with a label.
Indent remaining lines by four spaces if they are indented at any level.
Indent so that shellcrafts prettyfier will work.
Handle case with colon inside comment
First non whitespace characters in a label is alphanumeric.
'.' and '_' should be considered legal label characters too.
More elegant check for ':'.
Merge pull request #91 from RobertLarsen/master

Indent correctly for more cases