Bug fix in ScalarEncoder - 0s are allowed

The range would not be set correctly when minVal or maxVal was 0.  I
can't find any requirement that they not be, and this caused issues for
the ScalarEncoder with minVal = 0 and the LogEncoder with minVal or
maxVal = 1.
Adding LogEncoder and LogEncoderTest
Merge pull request #122 from wlmiller/add_logencoder

Add LogEncoder