Removed TK_FOR

Minor cleanup after #45, removing the token symbol as well.
Comma as a statement delimiter deprecated

The compiler now issues a warning if ',' is used as a statement
separater, but still allows it.

The built-in voice driver programs now use ';' instead of ','.

Closes #58.
Demo songs updated after compiler changes

Demo songs no longer use the removed 'run' statement.

Demo songs now use ';' instead of the deprecated ',' for statement
separator.

This is a cleanup after #45 and #58.