Add SyslogLogger

The SyslogLogger logs in syslog format according to RFC 5424.
Merge pull request #294 from jkm/sysloglogger

Add SyslogLogger
Don't compare with a constant when its a parameter.

Enforce that the address isn't longer than max_length instead of a constant that is only the same as the default.
Allow conversions of const(Task) -> Task.
Fix compilation on Windows and handle debugv/trace messages gracefully in the SyslogLogger.
fix warning

log.d(520): Warning: statement is not reachable
Merge pull request #300 from japplegame/patch-1

fix warning
Add UTF-8 validation for Bson.opAssign(string). See #299.
Remove the optional do_flush argument from OutputStream.write.

In order to approach the exact same behavior of standard blocking I/O, the do_flush parameter has been removed. Flushing now has to be done using an explicit flush() call if necessary.
Merge pull request #296 from MikeWey/patch-1

Don't compare with a constant when its a parameter.
Fix compilation.
Add IsolatedRef.opCast to allow safe conversions with move semantics and use in boolean expressions.
Remove useless static assert.
Update doc comments to mention render!() is supposedly safe on DMD 2.064.
Remove apt based installation instructions for DUB.

Installation instructions for DUB are already in DUB's readme and do not need to be duplicated here.
Implement HTTPClientResponse.disconnect().
Improve documentation of the vibe.http.client module.
Use explicit bind addresses in all HTTP server examples. See #8 and #298.
Fix compilation of the libevent driver on Win64. See #304.

Note that there are still no import libraries for libevent/Win64.
fix serialize to Json/Bson for const struct classes