grade.pl: added colors to output in different errors when reading
	  optical file.
mat2457-2013-optica-p{1,2}-t01.dat: renamed to match new pattern.
mat2457-2013-optica-p{1,2}-t01.dat: renamed to match the new pattern.
mat2457-2013-optica-t1-p{1,2}.dat: these are now mat2457-2013-optica-p{1,2}-t01.dat
.gitignore: fixed entry for dat and html final files.
mat2457-2013-optica-p{1,2}-t01.dat: modified to provide an example where
				    the set of students making each test
				    is different.
.gitignore: fixed pattern in output files from grade.pl
./merge_table.pl: this program basically merges to files, the first one
		  containing the student id and its current grades on
		  performed tests (- if it didn't how up) on each line
		  and the second one containd student id and his latest
		  grade.
merge_table.pl: fixed bug related to students that didn't show up in the
		first exam. Need to modularize all the repeated code there.
grade.pl: commented out most of the output parts, which are being moved to merge_table.pl.
grade.pl: removed all of the code related to merging grade files and
	  creating final html files. This job is noedone by
	  merge_table.pl
./merge_table.pl: improved formatting in HTML output table.