Add ASCII85 decoding

[gregorni]

Related to #61

Feedback is welcome!

[SkeletalDemise]

Add more tests for base85 vs ascii85. There should be tests to make sure this only decodes ascii85 and not base85. Also add tests with longer strings and special characters in the plaintext. See the base64 URL tests for an example.

[gregorni]

Can you give me a base85 string that isn't ascii85? All the online decoders seems to use the same encoding mechanism for both.

[bee-san]

cargo fmt fails :(

[bee-san]

Ahhhh looks like it's just clippy left!! :)

error: this is an outer doc comment and does not apply to the parent module or crate
Error:  --> src/decoders/ascii85_decoder.rs:1:1
  |
1 | / ///! Decode a ascii85 string
2 | | ///! Performs error handling and returns a string
3 | | ///! Call ascii85_decoder.crack to use. It returns option<String> and check with
4 | | ///! `result.is_some()` to see if it returned okay.
  | |___________________________________________________^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#suspicious_doc_comments
  = note: `-D clippy::suspicious-doc-comments` implied by `-D warnings`
help: use an inner doc comment to document the parent module or crate
  |
1 + //! Decode a ascii85 string
2 + //! Performs error handling and returns a string
3 + //! Call ascii85_decoder.crack to use. It returns option<String> and check with
4 + //! `result.is_some()` to see if it returned okay.
  |

error: could not compile `project_ares` (lib) due to previous error

[gregorni]

So now all the test pass, except the test suite which gets cancelled for taking too long.