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.
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].
Convert User::FormatNoticeMasks() to use std::string.
Convert User::SendText to use std::string.
Convert a ton of uses of MAXBUF to use a fixed buffer size.
Rewrite Channel::UserList to use std::string.
Remove hardcoded MAXBUF constant.