Link to the PHP manual for array functions
use a definition list instead of ad-hoc markup for definitions
Types section cleanup:

- Some rewording
- Modern PHP style prefers lowercase null/true/false
- Move contstants to constant section
Merge branch 'types'
Rewrite star/end tags for clarity
Port pull #46 - Further closure clarity
Merge branch 'pull-request/50'
__halt_compiler description
Constants fixes
Better explanation of scopes
Updated Namespace Use Declarations
- Included an example for absolute qualified names vs. relative names
- small typo
Updated statements.md
- replaced opt with <sub>opt</sub>
- some typos
Update README.md - made it more user friendly
It is nicer to have actual links then copy and paste the urls
Remove duplicated sentence about auto memory management.
Changed indentation from 4 to 2
Fix some typos.
changed indentation to blockquote
Merge branch 'constants'
Merge branch 'pull-request/58'
Markdown added to Basic Concepts