added "bgColor" fontStyle, "exactHeight" tableRowStyle and minor modifs for php://output

added "bgColor" fontStyle, "exactHeight" tableRowStyle and minor modifs for php://output

BGCOLOR:
- Meant to replace fgColor, can use any hex color instead of the 15 color constants in Font.php
- usage: ```$section->addText(" myText ", array("bgColor" => "112233"));```
- I found out that spaces after words cannot be highlighted (the same happens with fgColor)
my temporary fix is replacing all space with the htmlCode of a space so if you really need this feature, add this around line 78 in Word2007/Base.php, just before $objWriter->writeRaw($strText);
```$strText = str_replace(" ", "&#160;", $strText);```
- sample is in samples/Sample_20_BGColor.php

TABLE ROW STYLE EXACTHEIGHT
- added exactHeight for table row styling
- mostly for removing the auto-added space after elements in a cell
- usage: ```$table->addRow($height, array("exactHeight" => true));```
- sample is in samples/Sample_21_TableRowRules.php

MODIFS PHP://OUTPUT
- Tmp file should go into sys_get_temp_dir() instead of "./"
- added content-length header to get the total filesize when downloading