Unit sprites should have multiple frames

[ozkriff]

At least:

• IDLE
• Attacking
• Dead

Spearman should have multiple (3?) attack frames for different directions.

[ozkriff]

Waiting for #115

[ozkriff]

Made some progress:

Though I don't like how it looks (yet?).

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UPD: another experiment that I don't quite like:

[ozkriff]

Spearman special attack frames are moved into #477 ("Spearman should have three attack frames")