Model optimization of schools model.
Mixed type implementations of mdivide_left.
Implement mixed types of mdivide_left_tri.
Implement mdivide_right_* in terms of mdivide_left, to allow them to use the new varis.
added fmod, fmin, fmax to fvar with tests
rstan makefile patch from issue 86
Implement determinant vari.
Implement log_determinant and build a specialized vari for it.  Added tests for log_determinant.
Small optimization in multi_normal.
added binomial_coefficient_log with tests to fvar
added binary_log_loss to fvar with tests
Reimplement multi_normal to avoid the cholesky decomposition.  Implement multi_normal_prec.
Expose multi_normal_prec to the modelling language.
Add some missing using statements in new multi_normal implementations.
added matrix handling to math error handling
Merge branch 'fvar' of https://code.google.com/p/stan
more to-do and some definitions in the doc
new implementation of multi_normal missed 0.5 term in front of log_determinant
removing unused code in comments
Merge branch 'master' of https://code.google.com/p/stan