Added an arena allocator

A page is a flexibly allocated structure of bytes, with a count of the
number of bytes already allocated (used) and number of bytes available
overall (available), with a pointer to the next page, if any.

heap_t is a linked list of pages.  One may allocate a requested size
off the heap which causes one of two things:
1) Either a page already exists with enough space for the requested
size, in which case that page's pointer is used as the base for the
requested pointer
2) No pages satisfy the requested size, so a new page is allocated
which is the new end of the heap.

Makefile

@@ -14,7 +14,7 @@ TERM_RESET:=$(shell echo -e "\e[0;0m")
 ## Lib setup
 LIB_DIST=$(DIST)/lib
 LIB_SRC=lib
-LIB_CODE:=$(addprefix $(LIB_SRC)/, base.c darr.c inst.c)
+LIB_CODE:=$(addprefix $(LIB_SRC)/, base.c darr.c heap.c inst.c)
 LIB_OBJECTS:=$(LIB_CODE:$(LIB_SRC)/%.c=$(LIB_DIST)/%.o)
 LIB_DEPS:=$(LIB_OBJECTS:%.o=%.d)
 LIB_CFLAGS=$(CFLAGS)