Install libxml-ruby

Must install libxml2-dev first ,otherwise there will be errors like

sudo apt-get install libxml2-dev
gem install -r libxml-ruby
sudo apt-get install libxslt-dev
gem install -r libxslt-ruby

Building native extensions.  This could take a while...
ERROR:  Error installing libxml-ruby:
ERROR: Failed to build gem native extension.

/usr/bin/ruby1.8 extconf.rb
checking for socket() in -lsocket... no
checking for gethostbyname() in -lnsl... yes
checking for atan() in -lm... no
checking for atan() in -lm... yes
checking for inflate() in -lz... no
checking for inflate() in -lzlib... no
checking for inflate() in -lzlib1... no
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.