Additional road network extractor that works in external memory.

Docs/3rdparty.txt

@@ -2,4 +2,5 @@ Third Party Libraries:
 
 Boost		1.37+
 kdtree++	0.7+	(0.62 does not work with g++ 4.0+)
-sparsehash 	1.4+
+sparsehash 	1.4+
+stxxl		1.2.1+

Docs/FAQ.txt

@@ -34,4 +34,11 @@ Q: How fast is this thing?
 A: Good question. Here is a number. The engine was able to handle more than
    2800 requests per Minute on the German road network with the travel time
    metric on a Core 2 Duo. This also includes transfer of data across a 
-   switched 100MBit/s LAN. So, I guess it's fair to say it's fast.
+   switched 100MBit/s LAN. So, I guess it's fair to say it's fast.
+   
+Q: What is the difference between extractNetwork and extractLargeNetwork?
+A: extractNetwork does all of its magic in RAM, while extractLargeNetwork uses the
+   stxxl library to store the data in external memory. Use the first one for small
+   networks, but beware of running out of RAM. Swapping is the kiss of death. For
+   larger networks use extractLargeNetwork. It will be somewhat slower on the 
+   smaller files, but way faster with large ones like the planet file.

Docs/Todo.txt

@@ -8,5 +8,3 @@ The server part is mostly adapted from the boost http examples. It should be rep
 The KD-Tree uses a lot of RAM. An own implementation might be better.
 
 Use Boost to compress all in-/output streams to the file system
-
-Rework extractor to be fully externalized