align after function

[burnt43]

Just like in #3 I want to align, but this time the align should be on the first non-white space character after a character. For instance in a ruby hash

{
  key1: something,
  key100: something,
  key10000000: something,
}

I would like it to look like

{
  key1:        something,
  key100:      something,
  key10000000: something,
}

This means I align after the colon character.
The mapping prefix should probably be like <leader>ala (ALIGN AFTER)