Add module descriptions for the driver implementations.

source/eventcore/drivers/epoll.d

@@ -1,3 +1,9 @@
+/**
+	Linux epoll based event driver implementation.
+
+	Epoll is an efficient API for asynchronous I/O on Linux, suitable for large
+	numbers of concurrently open sockets.
+*/
 module eventcore.drivers.epoll;
 @safe: /*@nogc:*/ nothrow:
 

source/eventcore/drivers/posix.d

@@ -1,3 +1,8 @@
+/**
+	Base class for BSD socket based driver implementations.
+
+	See_also: `eventcore.drivers.select`, `eventcore.drivers.epoll`
+*/
 module eventcore.drivers.posix;
 @safe: /*@nogc:*/ nothrow:
 

source/eventcore/drivers/select.d

@@ -1,3 +1,10 @@
+/**
+	A `select` based event driver implementation.
+
+	This driver works on all BSD socket compatible operating systems, including
+	Windows. It has a good performance for small numbers of cuncurrently open
+	files/sockets, but is not suited for larger amounts.
+*/
 module eventcore.drivers.select;
 @safe: /*@nogc:*/ nothrow:
 

source/eventcore/drivers/timer.d

@@ -1,3 +1,6 @@
+/**
+	Efficient generic management of large numbers of timers.
+*/
 module eventcore.drivers.timer;
 
 import eventcore.driver;