Fixed highlighting issues in The Book
Added information about currency format
Add a clarification to the event subscriber section

It's not explicitly clear that a higher priority number means the method is called earlier. Add some verbiage to that effect.
Fix two minor typos in the contributing section
[2.0] Re-working some language in the contributing doc to work now that we have 2.0, 2.1, 2.2 and master
Merge pull request #2274 from WouterJ/issue_2273

[#2273] Add valid values for currency
[#2277] Backporting typo to 2.0 thanks to @pborreli
Merge pull request #2280 from jbafford/contributing-fix

Fix two minor typos in the contributing section
Merge pull request #2281 from jbafford/components-event_dispatcher

Add a clarification to the event subscriber section
[#2281] Slight language tweak
[#2282] Adding some linking, thanks to @WouterJ
Merge pull request #2282 from symfony/doc-contributing-version-bump

[2.0] Re-working contributing language for 2.2 branch
Unclosed parenthesis by PHP code-block
Merge pull request #2265 from WouterJ/fix_highlighting

[Book] Fixed highlighting issues
[#2265] Slight revert per @Stof
[#2216] Backporting some missing use statements
Merge branch '2.0' into 2.1

Conflicts:
	book/doctrine.rst
	book/propel.rst
	book/security.rst
	cookbook/form/use_virtuals_forms.rst