Removed git clean -xfd from top level Makefile

Too many students may shoot themselves in the foot if git removes
everything not under version control every time they merely want
to udpate the documentation.
Update README to reflect new directory structure
Extend with nontrivial instance
Typo in pagerank description
Merge pull request #2 from gustavcedersjo/master

Typo in lab description for the Pagerank lab
Clarify dangling vertices
More perspective
Fix number of vertices in three.txt
Clarify column structure of D and 1
10 top hits -> 5 top hits (for typographical reasons)
Rainbow perfect matching lab
Data files for testing
Small fixes including images, references
Python module for det over GF(p)
Determinant code for Matlab, C, Java
Include rev info in lab description, update Makefiles
Marking lab added
Fixed runtime for N=1023 in R1