Suboptimal folding

Introduced hooks into subopt. This function can find suboptimal folds
in a free energy value neighbourhood of the minimum free energy.

It requires the definition of an array of structs (SOLUTION*) for
obtaining the results.
Memory deallocation

Introduced a mechanism for memory deallocation. Particularly subopt can
return a large number of results (occupying a big portion of memory) so
all c allocated memory must be fretted.

When returning a c_char_p, ctypes automatically converts it to a
string. This prevents the possibility of free’ing it. An alternative is
to return a c_void_p and casting it to a string when needed, keeping
around the c_void_p for deallocation.
Repackage as package

Introduced init and version files to allow library to work as a package
with a clean interface (the namespace is not polluted by ctypes and os).
Merge branch 'develop'