add gpm2 software

Signed-off-by: Nico Schottelius <nico@kr.ethz.ch>

software/gpm2.mdwn

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+You know, gpm is a hack.
+
+The idea of gpm2 is to be a nicer hack:
+
+ * Support multiple mice
+ * Do not draw stuff, but write gpm2 client to do so (os/terminal specific stuff)
+ * Usable under different OS
+ * Allow hotplugging of mice (i.e. gpm2d can run without any mice at startup)
+
+## Trying out gpm2
+
+gpm2 is in its early design stage, but can so far display movement of a
+ps/2 compatible mouse.
+
+    git clone git://git.schottelius.org/gpm
+    cd gpm
+    git checkout -b gpm2 origin/gpm-2-hack
+    ./gpm2hack.sh /dev/input/mice
+    # move the mouse
+    # press enter key to end demonstration
+
+If you do not see mouse movement deltas, either your mouse in connected
+to a different device or you probably do not have permissions to communicate
+with it.
+
+## Development
+
+### Names
+
+ * gpm2_*: Stuff that may appear in a library
+ * *: Stuff that will only be used in the gpm2 main process
+
+## Mouse protocols
+
+Protocols in gpm2 are *not* part of the main system. Instead,
+each protocol is implemented in its own binary, which is called
+from gpm2d.
+
+This prevents to create just another ugly "static" struct array
+or the need to dlopen() and friends.
+
+### Implementing a protocol
+
+If you want to implement a mouse protocol, there are some things
+to take care of:
+
+ * You have a free choice of the programming language
+ * gpm2d will exec() gpm2-<protocol> from its path,
+ * gpm2d will connect stdin stdout of gpm2-<protocol> to the device file
+ * gpm2d will connect stderr to gpm2d, so gpm2-<protocol> can send messages
+ * gpm2d can drop priviliges to a specific, non-root user
+ * gpm2d will send SIGTERM to gpm2-<protocol> to signal normal termination
+  * gpm2-<protocol> should close the file and exit
+ * gpm2-<protocol> reports about events via stderr
+
+### Reading options from gpm2d
+
+If at some point gpm2d needs to pass protocol options to the protocol
+handler, they can be found in GPM2_PROTO_OPTS.
+
+## Client protocols
+
+Clients for gpm2 do not need to be c programs, but can be of any kind.
+The communication is a simple ASCII stream.
+
+### Connect to gpm2d
+
+Clients need to open /var/run/gpm2/gpm2d.sock to connect to gpm2d.