Tagging first stable release on the 4.0 branch

After several months of work, TDBM 4 is finally deemed stable!
A big thanks to all the team who tested it thoroughly.

Link to the release announcement

Adding logging capabilities

with a new PSR-3 logger that can be natively throttled

Bugfix release

Fixing bug in findFromSql method

Adding support for special JOINs

through the findFromSql function that let's users add custom JOIN clauses.

Fixing setting datetime/casted types to null

See #83

Fixes non protected column names

and changes cache mechanism to support installs that have no APC

Bugfix release

Merge pull request #79 from marcteyssier/4.0

Fix cache pivot table

Fixing json encoding of maps

Merge pull request #78 from nguyenk/4.0

fixing map iterator json_encode()

Fixing setting foreign keys to null

Merge pull request #74 from nguyenk/4.0

fixing cascade bugs on saving a bean with null FKs

Allow setting a nullable FK to null

Merge pull request #73 from moufmouf/4.0

 	Fixing the ability to set a column to null