Expand Dotfile syntax support to not require a <source> argument

Supported action syntax:

- `<action>: <source> -> <target>`
- `<action>: -> <target>`
- `<source> -> <target>`
- `-> <target>`

test/lib/internals/compile-dotfile-test.sh

@@ -39,6 +39,15 @@ dotify-action link ackrc .ackrc
 dotify-action link gitconfig \".gitconfig\""
 
 
+# Compiles standard actions without a <source>
+echo -e "root_link .dotfiles
+link: -> .ackrc
+link:-> \".gitconfig\"" > $dotfile
+assert "compile-dotfile $dotfile" "root_link .dotfiles
+dotify-action link .ackrc
+dotify-action link \".gitconfig\""
+
+
 # Compiles default (shorthand) actions
 echo -e "root_link .dotfiles
 link: ackrc -> .ackrc
@@ -48,6 +57,15 @@ dotify-action link ackrc .ackrc
 dotify-action default gitconfig \".gitconfig\""
 
 
+# Compiles default (shorthand) actions without a <source>
+echo -e "root_link .dotfiles
+-> .ackrc
+ -> \".gitconfig\"" > $dotfile
+assert "compile-dotfile $dotfile" "root_link .dotfiles
+dotify-action default .ackrc
+ dotify-action default \".gitconfig\""
+
+
 # Correctly indents actions
 echo -e "root_link .dotfiles
 if [ true ]; then