added image file check for background images
Add App#gutter
Use reported size of scrollbar
Fix mock gutter
images not found does not raise error
now unfound images do not raise an error
Merge branch 'no-file-error' of github.com:presidentJFK/shoes4 into no-file-error
removed pry
Refactoring TextBlockPainter to make links easier

The existing TextBlockPainter logic assumed that we only had a single
underlying text layout object to interact with. As such, methods treated
styling as one operation when some apply to all layouts equally, others to only
one of the layouts at a time.

This changeset splits those apart so the defaulting of styles across both
layouts happens in one set of methods, changes that are specific to a given
layout in others.

There was also some renaming to make better sense of what's happening. Names
were a bit generic--coming in it wasn't clear why set_font_styles was different
from set_text_styles, but they are actually dramatically different things. The
new names hopefully convey that more clearly.
Add #displace, with specs and sample
Adding class for collection of fitted text layouts

We'll start treating them as a group for any operations (styling, cursor and
link positioning) that will require spanning across the multiple separate text
layout segments.

This commit attempts to just add/extract some of the basic classes, but doesn't
start putting them into use in the main painter classes yet.
Apply default styles to text blocks via collection

This moves over the main drawing call and default styling application to the
FittedTextLayoutCollection.
Fix ParentDimensions so it also delegates margin_* calls

* helps with the rest of #533
* had to turn Dimension margin variables to be nil of not set
  instead of 0 so I could check if a value has been explicitly
  set or not for the dimension
* now better background layouting/more real
* value_modified? necessary to call the super method not just
  blindly return the instance var
good-vjot basically works - no need for the adjusted version anymore
Apply styling to segments within layout collection

This first commit moves towards applying segment styling (from sub-spans, links,
etc) when working against multiple layouts. This isn't wired in yet, doesn't
do actual styling, but gets the iteration in place properly for selecting
the ranges and layouts to work against.
Merge styles together on segment before applying

A range can potentially have multiple styles applied to it, so apply all of
them starting from the default style before actually setting the style.
add unit tests for the ParentDimensions still calling complex super methods
Fix bug for simple_form not starting up anymore #526
Further specs for previously unvocered color DSLHelpers test
@__app__ has the current_slot, not the app instance, correct call, fix #603