Fix bool on CentOS 6 (my-mail-ru#3)

Swift 4.0

Release 1.0.0

Add macOS compatibility

SampleXS is outdated, tests are better

Swift 3.1 compatibility part 2

Improve exception passing from Swift to Perl

Set UTF-8 flag only on strings containing wide characters

Better workaround for non-final class conformance to PerlSvConvertible

* Replace static method returning Self with initializer. It is much
  cleaner from outside and works without hacks for non-final classes,
  but a little bit strange inside as in some cases it doesn't initialize
  object but steals another.
* Underscore requirements of PerlSvConvertible - their are internals
  forced to be public by protocol.

PerlScalar is Hashable