tiny images are poorly intensified

[cdanis]

• offsets used in side-shaving intensification are currently fixed to 10px, and taking 10px off the edges of e.g. a 32x32 image produces garbage
• other intensification modes are needed, like adding a transparent border / background-colored-border* and then intensifying

*: this is hard

[cdanis]

more verification is needed (e.g. on not-transparent inputs) but adding a larger logical screen using gifsicle to create an effective border has done well on at least one test case