Move LogLevel enum from filelogger to logger.
Move LogHeader to LogStream.
Purge a ton of code related to non <log> related logging.

- InspIRCd::OpenLog
- ./inspircd --logfile [file]

This is no longer needed now we have (since 1.2) custom logging.
Accept a LogLevel instead of an int in logging methods.
Fix spacing in calls to LogManager::Log.
Remove OnUserPreNotice and OnUserNotice hooks, add MessageType argument to OnUserMessage and OnUserPreMessage

All modules (except m_nonotice) that perform filtering on messages have common logic for handling PRIVMSGs and NOTICEs and most of them run the exact same code in both cases
Add support for detecting C++11 variadic templates.
Merge pull request #548 from SaberUK/master+variadic-templates

Add support for detecting C++11 variadic templates.
Fix msvc detection of variadic template support
Convert XLine::Displayable to return a std::string.
Merge pull request #522 from SaberUK/master+xline-displayable

Convert XLine::Displayable to return a std::string.
Merge pull request #545 from SaberUK/master+logging-cleanup

Clean up the logging system (part 1 of 2).
Start to replace MAXBUF with <limits:maxline>.
Reserve ServerLimits::MaxLine instead of MAXBUF.
Compare to ServerLimits::MaxLine instead of MAXBUF.
Use iostream instead of C-style file operations.
Use InspIRCd::Format instead of snprintf().
Replace some C string operations with the + operator.
Rewrite irc::sockets::sockaddrs::str() completely.

- Replace use of MAXBUF with INET_ADDRSTRLEN/INET6_ADDRSTRLEN.
- Replace use of sprintf with InspIRCd::Format.
Convert ConvNumeric() to use std::string instead of char[MAXBUF].