Replaced tomo.Image with tomo.Canvas and tomo.Pattern

This is the first step in transitioning the API over to the new
design. The new tomo.Canvas interface gives drawing functions
direct access to data buffers and eliminates overhead associated
with calling functions for every pixel.

The entire artist package will be remade around this.

theme/theme.go

@@ -3,7 +3,6 @@ package theme
 import "image"
 import "image/color"
 import "golang.org/x/image/font"
-import "git.tebibyte.media/sashakoshka/tomo"
 import "git.tebibyte.media/sashakoshka/tomo/artist"
 import "git.tebibyte.media/sashakoshka/tomo/defaultfont"
 
@@ -151,34 +150,34 @@ func InputProfile (enabled bool, selected bool) artist.ShadingProfile {
 
 // BackgroundImage returns the texture/color used for the fill of
 // BackgroundProfile.
-func BackgroundImage () tomo.Image {
+func BackgroundImage () artist.Pattern {
 	return backgroundImage
 }
 
 // RaisedImage returns the texture/color used for the fill of RaisedProfile.
-func RaisedImage () tomo.Image {
+func RaisedImage () artist.Pattern {
 	return raisedImage
 }
 
 // InputImage returns the texture/color used for the fill of InputProfile.
-func InputImage () tomo.Image {
+func InputImage () artist.Pattern {
 	return inputImage
 }
 
 // ForegroundImage returns the texture/color text and monochromatic icons should
 // be drawn with.
-func ForegroundImage () tomo.Image {
+func ForegroundImage () artist.Pattern {
 	return foregroundImage
 }
 
 // DisabledForegroundImage returns the texture/color text and monochromatic
 // icons should be drawn with if they are disabled.
-func DisabledForegroundImage () tomo.Image {
+func DisabledForegroundImage () artist.Pattern {
 	return disabledForegroundImage
 }
 
 // AccentImage returns the accent texture/color.
-func AccentImage () tomo.Image {
+func AccentImage () artist.Pattern {
 	return accentImage
 }