Add solver "lmdif.f"

Add "lmdif.f",
  which is a Least-Squares solver
  based on Levenberg-Marquardt Algorithm.
Minor modification in testing program

Set default real KIND to 8 in "makefile".
Change "Tol" to 1e-10 in "test_rkf45.f90".
Make variable name "Num_Unit" capital.
Hide working array in "Ode_Result_sub"

Modify subroutine "Ode_Result_sub" in "Linear_Ode_mod.f90":
Delete input argument "Work_R","Work_I",
  which are working array passed to rkf45-solver.
Add input argument "Info","Num_Fun" to record
  iflag and number of function evaluations in each step.
Merge branch 'lm'
Merge branch 'rkf'