[ucd] [char] [utils] Make libraries no_std

[behnam]

Most of the transition was a matter of changing the namespace from std to core.

• Unit tests for Display implementations are moved into integration tests, allowing use of format!() in test code.

• [char-range] needed special attention, because of having an API using std::collections::Bound as input. Although the datatype is safe for core, it's part of liballoc APIs and therefore not available in libcore. Therefore, a new std feature is added to the package, which enables the part of the API.

• [char-range] Feature implementations are refactored into separate files to simplify configuration conditioning.

• [char-property] To be able to be used in no_std libraries, had to bring in some code for ASCII-case-insensitive char and str matching.

• [char-property] The char_property!() macro now depends on the caller package to include extern crate core; explicitly iff it's a normal (use-std) package.

Tracker: https://github.com/behnam/rust-unic/issues/144

[behnam]

bors: r+

[bors[bot]]

Build succeeded

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