XBW implementation

Author: Francisco Claude <fclaude@cs.uwaterloo.ca>

This xbw implementation considers only the tree generated by the xml (tags and attributes), the
text is not represented and the index doesn't replace the original xml file. The implementation
requires libxml++2.6, for installing it in ubuntu do:

        sudo apt-get install libxml++2.6-dev libxml++2.6-2 libxml++2.6-doc

This code was writen while visiting Sebastian Maneth and Kim Nguyen in NICTA, Sydney, Australia. 

Example of use:

$ ./gen_xml -f 1 > test.xml
$ ./parser text.xml index
$ ./engine index
> help

  Valid commands: 
  - help: shows this message
  - //a/.../b: searches for path a/.../b
  - size: shows the index size
  - quit: finishes the program
  - exit: finishes the program

> //keyword

  (results: 69969 | time: 11.2871ms | index size: 6590Kb)

> size

  Index size: 6590.83Kb

> quit

$