Polish Rspotify

[ramsayleung]

Clean up Rspotify, take some points of #127 into consideration.

• remove convert_map_to_string and convert_string_to_map in util.rs, replaced them with Reqwest's query method and Url struct.
• Many functions like Spotify::tracks take in a Vec<&str>/Vec/&[String]/&[&str], when they should take in an impl IntoIterator<Item = &str>.
• Split single senum.rs file into a module named enums and move it into model module.
• reexport struct in model module to allow users to write rspotify::model::FullAlbum instead of the overly verbose rspotify::model::album::FullAlbum.
• Rename CurrentlyPlaybackContext to CurrentPlaybackContext.
• Change release_date_precision to enum.

[ramsayleung]

@marioortizmanero I think this PR is ready to review, as for the rest of issues mention in #127 which are mostly about Model, I prefer to create a new PR, otherwise this PR will grow up to be a huge one which is difficult to review.

[marioortizmanero]

The thing is that I'm doing tons of changes at #129, specially related to the endpoints, so the merge conflict is going to be quite big if we use this right now. #129 is almost ready as well, can you start taking a look in there? If you can help me to update the docs and tests it'd be super useful.

[ramsayleung]

#129 is almost ready as well, can you start taking a look in there? If you can help me to update the docs and tests it'd be super useful.

Yeah, Sure. I am gonna to review thie PR, and collaborate to update docs and tests :)

[ramsayleung]

I have refactored enums module with strum crate, reduced line-of-code from 7396 to 6972, generated by tokei. It's much clear and readable than before, but we have introduced a new dependency, I think about that will it increase the compilation time ? The number of compilation units increased from 159 to 163 with default feature.

[marioortizmanero]

That's great! Have you measured the compilation times, rather than the number of units? IMO this dependency is worth it because it just removes so much boilerplate, and boilerplate is prone to bugs.

[ramsayleung]

Yes, I have measured the compilation times in my laptop with Intel i5-4200M:

git checkout 72c6ee3 # the last commit without `strum` crate.
> hyperfine --warmup 2 'cargo clean && cargo build --no-default-features --features client-reqwest' -i
Benchmark #1: cargo clean && cargo build --no-default-features --features client-reqwest
  Time (mean ± σ):     86.715 s ±  3.165 s    [User: 276.518 s, System: 14.973 s]
  Range (min … max):   82.019 s … 91.968 s    10 runs

git checkout ramsay_clean_up_rspotify 
> hyperfine --warmup 2 'cargo clean && cargo build --no-default-features --features client-reqwest' -i
Benchmark #1: cargo clean && cargo build --no-default-features --features client-reqwest
  Time (mean ± σ):     88.646 s ±  1.688 s    [User: 285.274 s, System: 15.676 s]
  Range (min … max):   84.932 s … 90.441 s    10 runs

And I think this PR is ready to be reviewed again :)

[marioortizmanero]

I think this is ready to be merged, if that's what you want.

[ramsayleung]

Merged :)

I think I will take times to cross off more items in #127 :)