Encryption (and more)

Made several changes/additions and did some housekeeping leading up to
implementing server list ping and authentication:

-Classes necessary for Minecraft encryption handshake and protocol
encryption are now implemented (AES128CFB8, SHA1).
-HTTPHandler class for making asynchronous HTTP requests added,
necessary for Minecraft authentication (introduces dependency on cURL).
-Started fleshing out the design for modules (see src/ping/main.cpp and
include/mod.hpp).  Have to make some additions to RLeahyLib for
cross-platform file-handling/-enumeration before I can move forward
here.
-Introduced URL encoding/decoding capabilities.
-Made some changes/improvements to the server, packet router, client,
client list, and send handle classes.
-Started reorganizing the server class so that it can be launched in
interactive or non-interactive mode.
-Fixed a bug in the MySQLDataProvider (one of the queries was errant).
-Added some constants to describe the Minecraft protocol version
supported to packet.hpp.
-Generated documentation for the first time, accordingly Doxyfile has
been added to the repo.