simplify asDouble and avoid the need for WITH_LIBTMB with by using

[boennecd]

… inline

change loop order in asSEXP and asMatrix (R matrices are in column major order)
fix #309

Notice that there is still a value function here:

adcomp/TMB/inst/include/tmb_core.hpp

Lines 803 to 818 in 52002f8

	/* FIXME: "Value" should be "var2par" I guess
	kasper: Why not use asDouble defined previously? */
	/** @name Value Functions
	Overloaded functions to extract the value from objects of various types;
	generally wrappers for CppAD::Value(x).
	@{
	*/
	/** Extracts the value of from TMB objects.
	\param x The variable to be extracted.
	\return Object of type double containing the value of the argument.
	*/
	double value(double x){return x;}
	double value(AD<double> x){return CppAD::Value(x);}
	double value(AD<AD<double> > x){return CppAD::Value(CppAD::Value(x));}
	double value(AD<AD<AD<double> > > x){return CppAD::Value(CppAD::Value(CppAD::Value(x)));}
	/** @} */

which can be changed to

template<class T>
double value(T const x)
{
  return asDouble(x); 
}

[kaskr]

Thanks for the PR - your changes make sense.

In case you make other changes I would kindly ask to split in many small commits.
Reason: There's a major restructure coming up (new AD framework - branch 'TMBad') and merging could become non-trivial if too much is done at once...