Add subroutine arguments in "linear_ode_mod.f90"

Add argument "Iter" in subroutine "OdeSolve",
to record number of derivative calculations.

Add argument "Info" in subroutine "OdeSolve",
to record status of each step.
Create "makefile"

For "linear_model_test.f90".
Modify ".gitignore"

To ignore data-files.
Fix bugs in "linear_ode_mod.f90"

Initialize "iwork" to 0.
Restore "iwork" to 0 in each iteration.

Fix a typo from "work" to "iwork".
Modify ".gitignore"

Not ignore data-files.
Use external data in "linear_model_test.f90"

Create "data".