fixed matrix_reorder bug, added nearest_neighbour and get_values

major bug in matrix_reorder (in which the sample names were
incorrectly rearranged during matrix reordering) has been fixed.

Nearest neighbour function pulls the (default) 10 nearest
neighbours to a specified gene, and prints them to file along
with some statistics about the average distance to all genes in
the data matrix.

Get_values class function will return the samples and their values
for a given gene.