Add a compiler for SpEL

With these changes an optional compiler is added for SpEL
expressions. The compiler is off by default but can be enabled
via the SpEL parser configuration object or system property
(when SpEL is embedded and parser configuration is not possible).
Not all expressions are currently handled but the common
cases are and it is an extensible compilation framework.

Issue: SPR-10943
Merge pull request #554 from aclement/SPR-10943

Add a compiler for SpEL