Image: Function formFile: Doc fix

Adding @throws
Merge pull request #7 from johnCourtier/patch-1

Image: Function formFile: Doc fix
more readable exception strings
typos
DateTime: createFromFormat() returns Nette\Utils\DateTime instance
Random: PHP bug 52523 has been fixed in 5.3.7
Merge pull request #6 from redhead/DateTime-fix

DateTime: createFromFormat() returns Nette\Utils\DateTime instance
Html: arrays in data-* attributes are encoded as JSON [Closes nette/nette#1399]

Before this commit they was encoded as CSS styles or space separated lists.
removed iconv_set_encoding()
readme.md: added badge and link to Packagist
composer.json: suggests fileinfo, mbstring and gd
composer.json: in conflict with nette/nette < 2.2
opened 2.3-dev
tests: removed @author
Image: added exception for error states [BC break]
tests: improved tests for images
Image::getFormatFromString() is deprecated
Html: added protection against innerHTML mXSS vulnerability [Closes nette/nette#1496] (possible BC break)

IE8 for code `<div attr="``foo=bar">` produces invalid innerHTML `<div attr=``foo=bar>`. Adding a space at the end of the attribute forces IE to put quotes around the attribute.

More info:
http://www.nds.rub.de/research/publications/mXSS-Attacks/
http://www.slideshare.net/x00mario/the-innerhtml-apocalypse
Json::encode uses JSON_UNESCAPED_SLASHES
FileSystem::isAbsolute simpler regexp