Refactored the logic of connection string generation

Change the name of the parameter instance_name by instancename

Hello, first sorry for my English. 
I need to put in the ORACLE Connection string to the parameter: (INSTANCE_NAME = XXXXX) 

I was reading the source code at github and the latest version does not include this possibility in the method getEasyConnectString. 

Could add to the next version an element in the array of parameters, eg $params['instance_name'] and concatenating that value to the Connection string? 

Thank you, greetings 
Facundo Panizza

- Fixed docblocks
- Removed return statements on void methods
- Cleaned up unused private / local variables
- Fixed license issues
- Removed SVN leftovers
- Fixed doctrine-project.org links
- Added line breaks before return statements

Fix bug where empty or null host connection parameter will still construct an Oracle DSN instead of using dbname.

to be able to make OCI8 derived classes

[2.0] More general work on the SchemaManager and Platform classes. Making API more complete and adding sqlite and mysql test coverage.

[2.0] Fixes and enhancements to sequence generators. Test suite now runs & passes against postgres. Other minor, unrelated cleanups.