[GR-2738] Update README and the documentation.

README.md

ci.hocon

...est/src/com/oracle/truffle/r/test/ExpectedTestOutput.test

.../oracle/truffle/r/test/library/fastr/TestJavaInterop.java

documentation/Limitations.md

documentation/README.md

documentation/README.md

documentation/allocprof.md

documentation/dev/testing.md

documentation/dev/truffle_llvm_ffi.md

documentation/graphics.md

mx.fastr/suite.py