Parser incorrectly requires colon for directives with arguments

[taasan]

The parser incorrectly treats the colon (:) as mandatory for directives that take arguments.

According to the ChordPro documentation:

For directives that take arguments, the arguments are separated from the directive name by a colon : and/or whitespace

This means both of the following should be valid:

{title: Harvest Moon}

and

{title Harvest Moon}