Support alternate JavaCompilers (such as ECJ) in JavaSourcesSubject

[doanduyhai]

New syntax to inject custom compiler:

    assertAbout(javaSource())
        .that(JavaFileObjects.forResource(Resources.getResource("HelloWorld.java")))
        .withCompiler(new EclipseCompiler())
        .withCompilerOptions("-nowarn", "-1.6")
        .compilesWithoutError();

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[doanduyhai]

I signed it!

[googlebot]

CLAs look good, thanks!

[tbroyer]

Would be even better if you somehow merged #71 into that one wrt passing a JavaCompiler to the CompilationRule rather than always using ToolProvider.getSystemJavaCompiler(). Sure one can easily be rebased on the other anyway…

[doanduyhai]

Sure, as soon as @tbroyer fixes the file manager thing

[tbroyer]

👍

Lacking tests running with the Eclipse compiler though to make sure everything works OK.

[gk5885]

Actually, I'd be happy to see this and #71 get merged into one p/r.

[doanduyhai]

Hello here, no new ?

#71 is still not merged yet so I'm stuck with my PR ...