Constructors & Destructors. Sample implementations.

Changelog:
 1. Constructors & Destructors:
  - Should be put inside .c files.
  - This avoids redeclaration of initialization and destruction functions.
  - Also accords to the analogous C++ system of constructors/destructors
    module separation thingy.
 2. Sample implementations:
  I. Vector
   o An (x, y) vector.
   o Basic arithmetic functions.
   o I'm ashamed (yet secretly proud) of some really kludgy work with
     stringization and token glueing.
   o You may alter the toString (decimal) precision by changing vector.c's
     PRECISION macro.
   o Uses String from string.h.
  II. String
   o Simple String class implementation.
   o Uses array redimensioning.
   o Simple setting, concatenating, resizing and cloning functions.

Bugs and Issues:
 - For some reason, when you run the example test.c source code, it
   sometimes crashes right at the end. I'm thinking it has something to
   do with delete. Not sure though. Further investigation is required. I
   can't let this crime go unpunished. There has to be a criminal here
   involved. It just can't be a coincidence. All pieces will come
   together. Soon.
 - When running the previous issue coupled with GDB, it won't crash.
   Weird. Creepy. Supernatural. Ghosts. Who we gonna call?