Features:
* STL-like interface
* Fast modification: no branches on insertion or deletion
* Fast iteration: one pointer dereference and one pointer comparison
* Your class can be a part of several lists

Modeled after std::list<T> but currently has fewer methods (not complete yet)

For even more performance it's possible to customize list with templates so
it won't have size counter variable or won't NULLify unlinked node.

How existing lists differ?

No existing lists support STL-like interface.

I_List:
* slower iteration (one more branch on iteration)
* element can't be a part of two lists simultaneously

I_P_List:
* slower modification (branches, except for the fastest push_back() case)
* slower iteration (one more branch on iteration)

UT_LIST_BASE_NODE_T:
* slower modification (branches)

Three UT_LISTs were replaced: two in fil_system_t and one in dyn_buf_t.