Addition of brainfuck implementation.

This requires the Kees Jan Koster Brainfuck compiler with process
extensions (BFPX): http://www.kjkoster.org/BFPX/Brainfuck_Process_Extensions.html

Yes, it works:

[~/Documents/bfpx-1.0] java -jar bfpx.jar samples/concur.b && java -cp bfpx.jar:. concur
40 + 70 + 20 = 130
[~/Documents/bfpx-1.0] java -jar bfpx.jar samples/concur.b && java -cp bfpx.jar:. concur
40 + 20 + 70 = 130
[~/Documents/bfpx-1.0] java -jar bfpx.jar samples/concur.b && java -cp bfpx.jar:. concur
70 + 20 + 40 = 130