Fix benchmarks for Julia 1.0 / 0.7

1) The benchmarks use depend on packages UnicodePlots and IndexedTables. IndexedTables is still not working on Julia 0.7, but the functionality can be referred from package Millboard instead.

2) The benchmarks also use logutils from the logging folder in this package. It probably does not work due to the new broadcast behaviour. Consider referring another logging package.

3) 'Open browsers' also needs some fixing for Julia 1.0. Consider including e.g. Blink.

4) Optionally expand benchmarks with tests. Second-per-byte is probably not the most interesting benchmark. Message latency or messages per second for various browsers / client is more interesting. It would also be interesting to compare the performance of various methods of running /compiling/ calling javascript. Also, how to avoid memory allocation -> garbage collection. The latter probably belongs in the example folder.