Let the get_files function skip excluded directories

[jianse]

this may help #233

following is an simple benchmark output

[hamirmahal]

This looks interesting.

I'm not a maintainer, but are you open to adding automated benchmarks to CI?

[jianse]

I add the benchmark at https://github.com/jianse/rust-embed/tree/benchmark . But it missing some example data to support it. see https://github.com/jianse/rust-embed/blob/0601a054c0d9971ff831e9919a4a78a34825c179/benches/walkdir_bench.rs#L8

after fix the example data problem. you can run cargo bench to get the benchmark result.

about the automation part. I am not familiar with it. so any help with be be appreciated.