fixed bug with mainlabel causing duplicate headers.

if mainlabel parameter was set to "Test", the first two columns in the
excel file would result in column headers like the following:

Test	Test#

This patch filters out the second column header Test#
Refactored the excel format for cleaner, more readable code.
Merge pull request #19 from netbrain/excel

fixed bug with mainlabel causing duplicate headers in excel format.
Made excel export format enabled by default
and added PHPExcel as a suggested library through composer

If PHPExcel is not installed, the excel export format will not be available
Improve check for PHPExcel being loaded

Before a file with references to non-loaded code would still get parsed,
that is not very nice.
Style improvements to excel format code
Merge pull request #22 from SemanticMediaWiki/enableexcel

Enable the excel format by default is it can be loaded
use getcwd() instead of exec('pwd')
Merge pull request #23 from addshore/master

use getcwd() instead of exec('pwd')