Minor changes and refactor

[victor-iyi]

Mostly containing style changes & refactor; including OpenSSL build requirement for Fedora and Ubuntu in README.md.

Some changes include:

• Added MythraResult<T> type, rather than passing Result<T, Box<dyn std::errror::Error>> around.
• Moved src/engine.rs to src/engine/mod.rs.
• Markdown rule updates for README.md.
• Bump version number & dependencies upgrade.

Roadmap:

• Implement engine traits. e.g impl FreeMP3Cloud for EngineTrait { ... }.
• To be moved from type.rs to engine/mod.rs.
• parse_single_music has return type Option while EngineTrait has MythraResult.
• Triat definition isn't pub async.
• Dedicated *music.rs mod including Music structs/traits implementations.
• Documentation with rustdoc.
• Match engine as enums on src/api.rs:18.
• Create *bulid.rs to handle OpenSSL versions and platforms.
• Simplification of utils.rs.
• Engine already matched in src/api.rs:search, it shouldn't be repeated in src/engine/mod.rs:search_all.
• download.rs:download_from_url should return a Result type indicating if download failed or succeeded.
• More error support required in *error.rs.