XLS file parsing performance imporvements

At the moment php-excel-reader library is partly rewritten so that it parses file in multiple steps:
1) It reads in memory Workbook, Sheet information, Formatting and SST values
2) For each sheet is calculated rows, columns and offsets and stored in memory
3) On each row iteration is checked is data available (isset($this->data[$this->Index]), if not then data is loaded from file (usually 32 records at a time, if such amount is available), if data is available then specified data are used. During those iterations position is kept when XLS file is parsed.

Other things:
- namespaces
- function in test.php to visualize size measurements (b, kb, mb ..)
- some simple unit tests for XLS file which compares formats

Known issues:
- formats not working very well for date and time 
- some of the unit tests may fail because of that