Reorganise configuration files:
- Example config files now end with .conf.example.
- Example text files now end with .txt.example.
- Removed 'inspircd' from the name of multiple example files.
- Added missing oper motd example file.
Merge pull request #430 from SaberUK/insp20+config-tidy

Reorganise configuration files.
cmd_lusers Convert to a module
cmd_lusers Refresh max local/global user counters after a user connects

Fixes #423 reported by @RawrDragon
cmd_lusers Use of size() instead of counting elements
cmd_lusers Be smart and know how many invisible users are there without iterating the userlist
Update Doxyfile for the latest version of Doxygen.
Merge pull request #437 from SaberUK/insp20+doxygen-update

Update Doxyfile for the latest version of Doxygen.
m_dnsbl Fix connecting users timeouting when a dnsbl result is in the dns cache

Fixes #431 reported by @killerrabbit
Stop user initialization when the user is marked as quitting after OnSetUserIP
Either store the Resolver in DNS::AddResolverClass() or delete it before returning
Fix m_dnsbl not checking cgiirc users when the cgiirc address is elined
m_connectban Switch to OnSetUserIP hook to handle cgiirc users properly, ignore e-lined users
Remove dead code from DNS
Replace Windows build system and installer with cmake
Modified m_timedbans to behave more like setting mode +b manually.
It now accepts extbans. If one enters something not an extban, or valid banmask, it'll add "!*@*", making it a nick-ban instead of borking.
m_ssl_openssl Make it clear that a CA file is not mandatory
Link win32_memory too inspircd too
m_connflood Ignore e-lined users
m_permchannels Load channels from the config only at module load time and only when there are no linked servers to avoid desync