Gem installation fails on Linux

[MaineC]

Following the suggested installation instruction from the README.md did not work on my Ubuntu 18.04 LTS box. It failed complaining that libxml-ruby is not installed (which it is). The trouble seemed to be related to something already addressed in #11 as well as in tonyfg/libxslt-ruby.git

Issuing on xml4r/libxslt-ruby master a

ruby ext/libxslt/extconf.rb

also resulted in the error

extconf failure: %s
      Need libxml-ruby
      Please install libxml-ruby or specify the path to the gem via:
        --with-libxml-ruby=/path/to/libxml-ruby gem

Commit 2ed8d55 from tonyfg/libxslt-ruby.git fixes this with extending the already existing hack for darwin to linux

After those changes, a gem build libxslt-ruby.gemspec fails with

Invalid gemspec in [libxslt-ruby.gemspec]: uninitialized constant Gem::Specification::DateTime
Did you mean?  Gem::Specification::DateLike
ERROR:  Error loading gemspec. Aborting.

This is fixed with commit 69bd5cc

Added documentation on how to build and install from source with 531d38f and cf69596

[cfis]

Sorry for the delay.