Fix no annotation issue

[zeileis]

Fixes #626

For compatibility with base R tinyplot(..., ann = FALSE) should suppress title and axis notation.

This is implemented now by passing the ann argument to draw_title() and only drawing title() and mtext() elements if ann = TRUE.

[grantmcdermott]

Thanks @zeileis. Two comments, one small and the other a potential efficiency gain. LMK!

[grantmcdermott]

Thanks!