Refactor examples

[nbelakovski]

In this PR I have:

• Added an example_1 to all Fortran examples with the trivial objective function $f(x_1, x_2) = (x_1-5)^2 + (x_2-4)^2$
• Minor modifications to CMake and Make files to accommodate two examples within the Fortran code.
• Modified the C examples to use the same trivial objective function and bring them in line with the Fortran examples

The goal is to provide at least one example using a trivial objective function (in this context 'trivial' implies that the optimal point of the function is obvious without having to take any derivative or do any math) so that the user can focus on the API and usage.

The previous C objective function was actually a little strange, its optimal point was $(2.99, 2 - \frac{1}{140})$ which is not obvious and looks close enough to $(3,2)$ that when the optimization algorithm settles on $(2.99, 1.99)$ it looks "close enough" when in fact it is exact (within the limits of finite precision).

[nbelakovski]

@zaikunzhang Any comments?

[zaikunzhang]

Thank you @nbelakovski . I made some small modifications to the examples:

https://github.com/libprima/prima/commit/c342289a014c29d6297efc153f20d9b9f12dd587 https://github.com/libprima/prima/commit/4347d535bee41bf08d022c8effcbc3b053d6c75f

I hope you agree with them. Tell me if this is not the case.

[nbelakovski]

Those mods seem fine to me, thank you.