Use EIFFEL_LIBRARY environment variable instead of EWF_HOME and CJ_HOME

The goal is to reduce the need to many per-project environment variable
(such as GOBO, EPOSIX, ...).
This was discussed on the mailing list before :
https://groups.google.com/forum/#!topic/eiffelhub/sheBaxKAMtk
Use GRAPHVIZ_DOT_DIR env variable to compute dot command
Avoid print, use io.error.put_string
Always initialize converters ..
use GRAPHVIZ_ROOT_DIR to guess document dir
extra handle for error
updated config file.
Merge branch 'master' into eiffel_library_env

Conflicts:
	graphviz_server.ecf
Improve the documentation: Requirements and Run

* Requirements: Graphviz
* Run: GRAPHVIZ_DOT_DIR environment variable
Merge pull request #5 from oligot/eiffel_library_env

Use EIFFEL_LIBRARY environment variable instead of EWF_HOME and CJ_HOME
Merge pull request #7 from oligot/doc

Improve the documentation: Requirements and Run
Merge branch 'master' of https://github.com/EiffelWebFramework/graphviz-server

Conflicts:
	graphviz_server.ecf