[BUG] Investigate the performance overhead of result types

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See discussion under #56 for detials

Just realized a different thing, I tried your benchmark with a CPU profiler.
The result is so shocking: 25% of the time is spend to handle the Result types.
I try to remove one question mark from the rasterizer, it turns out a 10% speed up.

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Local repo:

test sine_640_480                                  ... bench:   4,188,667 ns/iter (+/- 338,945)
test sine_640_480_2_horizontal_subgraphs_draw_both ... bench:   4,609,418 ns/iter (+/- 407,366)
test sine_640_480_2_horizontal_subgraphs_draw_one  ... bench:   2,298,113 ns/iter (+/- 461,527)
test sine_640_480_2_horizontal_subgraphs_fake_blit ... bench:     270,355 ns/iter (+/- 53,794)

0.2.8:

test sine_640_480                                  ... bench:   7,277,665 ns/iter (+/- 3,636,985)
test sine_640_480_2_horizontal_subgraphs_draw_both ... bench:   8,129,140 ns/iter (+/- 937,515)
test sine_640_480_2_horizontal_subgraphs_draw_one  ... bench:   4,303,821 ns/iter (+/- 255,423)
test sine_640_480_2_horizontal_subgraphs_fake_blit ... bench:     288,119 ns/iter (+/- 102,912)

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Update, I refactored two question mark to is_err it turns out 50% speed up.

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Related Rust issue: rust-lang/rust#37939