Add support for movability to random generators. Fix POSIX random provider

[Lastique]

The commit adds support for move constructors and assignment to random UUID
generators and random providers. Also, in POSIX random provider, the commit
improves handling of return value from ::read(), which returns -1
in case of error and may return 0 in case of success. Retry the call when
it was interrupted before reading any bytes from /dev/urandom.

Added new tests for movability.

This fixes #71

[jeking3]

Interesting that you chose to do this without boost::move, any particular reason?

[jeking3]

Ideally we should have a compile-fail test that attempts copy by constructor and another copy by assignment to make sure those are properly disabled. This would ensure in the future nobody re-enables it by accident.

[Lastique]

Interesting that you chose to do this without boost::move, any particular reason?

I did not want to pull in Boost.Move as a dependency. But if you think it's worth supporting move operations in C++03 then it can be added.

[jeking3]

I was trying to do it with Boost.Move but it wasn't cooperating with me. It was probably me though. :) I'd prefer it to be implementation that works with both language levels. The dependencies in move are pretty light:

https://pdimov.github.io/boostdep-report/develop/move.html

I also offered to help the maintainer of Boost.Move add CI to that repository when I found it had none.

[codecov]

Codecov Report

Merging #74 into develop will increase coverage by 1.43%.
The diff coverage is 77.19%.

@@             Coverage Diff             @@
##           develop      #74      +/-   ##
===========================================
+ Coverage    78.34%   79.78%   +1.43%     
===========================================
  Files           13       13              
  Lines          605      638      +33     
  Branches       156      154       -2     
===========================================
+ Hits           474      509      +35     
  Misses          17       17              
+ Partials       114      112       -2

Impacted Files	Coverage Δ
include/boost/uuid/random_generator.hpp	72.91% <68.96%> (+15.34%)	⬆️
...nclude/boost/uuid/detail/random_provider_posix.ipp	86.48% <85.71%> (+10.48%)	⬆️
include/boost/uuid/detail/random_provider.hpp	92.3% <85.71%> (+6.59%)	⬆️

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[Lastique]

I've added support for C++03 and compile-fail tests.

[MarcelRaad]

Works fine for me with VS 2017 Update 7.3 and Update 8 Preview 2.0.

[jeking3]

Would be nice to add a unit test for the EINTR handling at some point. Thanks for the help on move.