Update BaseDrawing.php

Avoid division by zero
DocBlock updates
Allow value of 0 to be passed into POISSON formula
Bug "Undefined variable: options"

There is a bug for the var `$option`:

    Notice: Undefined variable: options in [...]/vendor/phpoffice/phpexcel/Classes/PHPExcel/Settings.php on line 384

This bug is fixed with `self::$_libXmlLoaderOptions == (LIBXML_DTDLOAD | LIBXML_DTDATTR)` instead of `$options == (LIBXML_DTDLOAD | LIBXML_DTDATTR)`
change sequential validation for orientation dompdf
Prevent autoload clash when previous code has used spl_autoload_register
Merge pull request #368 from TravisPaul/develop

Prevent autoload clash when previous code has used spl_autoload_register
Change the names of variables $plotarea and $dataseriesLabel to $plotArea and $dataSeriesLabel, respectively, to make it camel case compliant
Merge pull request #377 from dmelo/develop

Change the names of two variables on the examples, to make it camel case
Implement empty ODF archive

Work item CP1930, GH-157
Implements basic writing functionality
Add example
Invalid Index

This happened when I tried to load an Excel doc that was exported by Google Docs. I'm guessing there is no author information or something? I dunno but this fixed worked.
Merge pull request #381 from shrimpwagon/patch-1

Invalid Index
Fixed bug on jpgraph dependencies (It's suggested to use composer jpgraph/jpgraph instead of requiring these files)
Reduce memory usage after an xls load
Merge branch 'develop' of https://github.com/PHPOffice/PHPExcel into develop
Merge pull request #352 from ke20/patch-1

Bug "Undefined variable: options"
Merge pull request #378 from frost-nzcr4/ft-157-ODF

Add basic ODS writing functionality
Merge pull request #349 from luxbet/poisson_fix

Allow value of 0 to be passed into POISSON formula