Create change_e_vbgf.r

Move code from Christine's vbfg_function.R to change_e_vbgf.r.
Original file included loading package and instructions to simulate data.
change_e_vbgf is used in change_e if an init value for a parameter is
listed as "change_e_vbgf". This allows complete back compatibility with
change_e. Just the documentation needs to be updated. Also if other
estimation routines are created it can use this same protocol as well
rather than adding function arguments for each routine. Need to make sure
that the functions included in change_e_vbgf are available to all other
functions in the package.
modify change_e == should work. start of testing.
Add bbmle as a dependent package.
working on change_e to use change_e_vbgf.r need some work on output and input from the outside estimation routine