Add no_std + alloc support

[Dentosal]

This pull request adds no_std + alloc support behind a feature flag, closing issue #15. It also updates tinyvec dependency, migrates code to 2018 edition of Rust and runs rustfmt on the codebase. Tests for both std and no_std versions are added to .travis.yml.

[Manishearth]

Could you please do these as separate commits?

[Manishearth]

newline at eof please

[Dentosal]

Separated to multiple commits, and added the missing newline

[Manishearth]

mod tables should have a #[rustfmt::skip], it's autogenerated and i'd prefer to have it be easily diffable

[Dentosal]

Added relevant #[rustfmt::skip] attributes.

[Manishearth]

No, please add it to the entire module, that file is generated and should not be manually edited. Please add it to the mod tables; in lib.rs

[Dentosal]

Done. I edited both the script and src/tables.rs manually, because https://www.unicode.org has been down for a few days now. The changes should still be identical.

The travis check seems to fail because of a network timeout when installing Rust.

[Manishearth]

There is still rustfmt::skip on individual items in tables.rs

[Dentosal]

Fixed

[Manishearth]

Thanks!

[Dentosal]

Thanks for patience. Please close issue #15 as this fixes it.