add bit reversal method of a 64-bit word
added path() method to wavelet trees and wavelet matrix
added symbol_eg and symbol_es functions with tests
renamed reverse method to rev and added tests
Added restricted_uniq_range_values

this commit adds the functionality to retrieve, in ascending order, all
unique values in a range [x_i,x_j] restricted by [y_i,y_j]. the
functionality is supported by all wavelet trees which are lex ordered
plus the wavelet matrix.
removed unnecessary comparison
renamed symbol_eg -> symbol_gte and _es -> _lte
Merge pull request #170 from mpetri/master

Add restricted_uniq_range_values , bits::rev, symbol_eg and symbol_es