Add support for compiling scripts & executing pre-compiled scripts.

[geoffreyharding]

Hi,
The goal of this change is to increase performance by precompiling the sanitized JS.
Use-case: an application which runs the same JS script many times, and requires low latency.

class Example
{
  NashornSandbox m_sandbox = NashornSandbox.create();
  CompiledScript m_precompiled = sandbox.compile("1 + 1");

  public int doSomething()
  {
     return (int)m_sandbox.eval(m_precompiled);
  }

[mxro]

Thank you that looks great! Will have a closer look at this by next weekend the latest.

[mxro]

Thank you for the PR - released with version 0.2.4 which should be available on Maven central soon!