[DCOM-96] Refactor ProxyGenerator to lazy templating and introduce AbstractProxyFactory.
Fixed an undefined variable.
Merge pull request #246 from BenMorel/varfix

Undefined variable fix
Applying fixes as commented on doctrine/common#247
Applying fix for tests breaking in <5.4, adding 5.5 to build matrix
Merge pull request #248 from Ocramius/hotfix/doctrine/common#247-fixes

Hotfix/doctrine/common#247 fixes
Merge pull request #247 from doctrine/ProxyFactory

[DCOM-96] Refactor ProxyGenerator, introduce AbstractProxyFactory