Fixes #89.

Fixes #62

More info about ARC architecture is here: [1] & [2].
We need ARC supported here for many things like:
 - ICU (see [3])
 - Qt5 etc

[1] https://www.synopsys.com/designware-ip/processor-solutions/arc-processors.html
[2] https://en.wikipedia.org/wiki/ARC_(processor)
[3] https://unicode-org.atlassian.net/browse/ICU-20155

Fixes #81

Large hex literals would lose their minus sign.

Fixes #49

Fixes #48.

This should make it easier to add new architectures.

Fixes #73.

Use `static_assert` with newer compilers.

Add Native Client as support architecture.

Fixes #67.

Fixes #66.

Avoid undefined cast to make ASAN happy.

Add `exports_files`

The LICENSE file wasn't exported.

* Clarify output charset in DoubleToAscii documentation

* Fixing typo in charset docs.

Rename macros.

Renamed DISALLOW_COPY_AND_ASSIGN and DISALLOW_IMPLICIT_CONSTRUCTORS to
DC_DISALLOW_COPY_AND_ASSIGN and DC_DISALLOW_IMPLICIT_CONSTRUCTORS.

This makes it easier to use this library in projects that have macros
with the same name (as is common in Google).

Some refactorings: remove unused static, replace deprecated headers, init member in constructor

Fix typo in variable name.

CMake fixes.

Implement ALLOW_CASE_INSENSIBILITY mode for StringToDoubleConverter c…