Fix build of version 0.20.0

[archeoss]

aHash version that we used was yanked. This breaks the build. As a solution we can copy the source code of a particular version of aHash into Pearl.

The following steps should be done:

1. aHash of version 0.7.4 should be copied (commit ffa04fcb81f39755f636c75c9b7aa06533c0ae75) to src/filter/aHash/ directory
2. Include copyright notice and particular version in the comment on the top of every copied file
3. Update the code to use the copied version of aHash
4. Verify that the calculated hash matches the ones that was calculated by the original version (this test should pass:
5. Verify that there is no observable performance degradation (by running pearl benchmarks)
6. Add test results for AHash in order to justify that specific hash function.

Comment on the top of every file can look like this:

// Original work: Copyright (c) 2018 Tom Kaitchuck
// Distributed under MIT license
// Taken from aHash version 0.7.4 (commit ffa04fcb81f39755f636c75c9b7aa06533c0ae75)