Fix bug preventing history from being returned
Fixed typo
Fix printing of random effects names in summary
Minor optimization for no_smw case
Optimize a bit by precomputing ex_re^2
Refactor parameter handling, improve starting values
Restored steepest ascent, with some modifications
Restored steepest ascent, with some improvements
Add todo about unequal group sizes
Use MixedLMParams to specify free/fixed structure
Merge pull request #1940 from kshedden/lme-docstring

REF: refactor and speedup of mixed LME