no change in behaviour.

It does not do much harm - but it causes an unnecessary (failing)
system call.

It was implicitly deleted since commit
db23c2f2

Needed for WStringView.

These will be generated by the compiler automatically.

This is not necessary, because a strlen() on a literal gets optimized
away by the compiler.

Coverity discovered that the Pulse plugin could throw exceptions from
Pause(), but that method was marked "noexcept" because its caller was
not designed to catch exceptions.  So instead of avoiding exceptions
(by catching and logging them in each and every implementation), let's
allow them, and do the catch/log game in the MPD core.

The "-1" magic value is deprecated now.

Closes #107