Use Logging module in tmcmc function

[FriesischScott]

I decided to use @info to log the beta value of the current iteration. The rest of the statements hold little value for the end user in my opinion so I used @debug to log them. Standard logging looks like this:

[ Info: β_1 = 0.016394779086112976
[ Info: β_2 = 0.06899239096730403
[ Info: β_3 = 0.23616091794255514
[ Info: β_4 = 0.6787443625386766
[ Info: β_5 = 1.0

The debug statements can be turned of by setting the JULIA_DEBUG=TransitionalMCMC environment variable.

┌ Debug: Beginnig iteration 1
└ @ TransitionalMCMC ~/src/github.com/AnderGray/TransitionalMCMC.jl/src/tmcmc.jl:39
┌ Debug: Computing likelihood with 1 workers...
└ @ TransitionalMCMC ~/src/github.com/AnderGray/TransitionalMCMC.jl/src/tmcmc.jl:45
┌ Debug: Computing β_j...
└ @ TransitionalMCMC ~/src/github.com/AnderGray/TransitionalMCMC.jl/src/tmcmc.jl:55
[ Info: β_1 = 0.015737786889076233
┌ Debug: Computing weights...
└ @ TransitionalMCMC ~/src/github.com/AnderGray/TransitionalMCMC.jl/src/tmcmc.jl:74
┌ Debug: Markov chains with 1 workers...
└ @ TransitionalMCMC ~/src/github.com/AnderGray/TransitionalMCMC.jl/src/tmcmc.jl:106

This way the tmcmc reports the progress without adding to much noise.

Closes #14

[AnderGray]

Thanks for this, I agree.

Although I think maybe the likelihood and Makov chain prints statements should be an info instead of a debug.
Do you know if there's anyway to change the verbosity of the logging?

[FriesischScott]

Statements like "we are now doing something" don't add a lot of value in my opinion. But since they might take some time depending on the problem it might not be too bad to show them. Want me to change them to @info?

You can disable output for everything below a certain log level with disable_logging(level) e.g. disable_logging(Logging.Info) will disable everything equal to info and below.

[AnderGray]

You're right, merged!