README.md: installation location update.
TODO.md: Updated todo list.
Makefile: O2 optimizations enabled by default.
Vector Implementation

Vector implementation has been added. This implementation has not been tested.

File(s):
   modified:   Makefile
   new file:   include/vector.h
   new file:   src/vector.c
TODO.md: removed vector from the list of structures.
Update: Linkedlist Implementation

Updated the underlying implementation of a linkedlist. Also updated the
implementation of the function ll_apply(...) to accept single argument
functions.

TODO:
 * Simple optimizations to make additions and removals faster.

File(s):
   modified:   include/list.h
   modified:   src/list.c
README.md: update.
Merge branch 'linkedlist'
Style update.
Merge branch 'vector'
src/list.c: ll_toarr(...): properly allocates array.
Merge branch 'linkedlist'