Rewrite RGBLINK entirely

The goal was to improve readability, but along the way a few things were
gained.
- Sorted sym and map files
- Infrastructure for supporting multiple .o versions
- Valgrind-proof, as far as my testing goes anyways
- Improved verbosity messages
- Added error checking
- Performance improvements, see end of commit message

The readability improvement was spurred while trying to make sense of the
old code while trying to implement features such as sorted sym and map
files.
I also did my best to remove hardcoded logic, such that modifications
should be doable; for example, "RAM loading" sections, which are linked
against a different location than the one they're stored at.

Some work remains to be done, see the "TODO:" and "FIXME:" comments.
Further, while regression tests pass, this new linker should be tested on
different codebases (ideally while instrumented with `make develop` and
under valgrind).
The few errors spotted in the man pages (alignment) need to be corrected.
Finally, documentation comments need to be written, I have written a lot of
them but not all.

This also provides a significant performance boost (benchmarked with a
51994-symbol project):

Current master RGBLINK:
2.02user 0.03system 0:02.06elapsed 99%CPU (0avgtext+0avgdata 84336maxresident)k
0inputs+11584outputs (0major+20729minor)pagefaults 0swaps

Rewritten RGBLINK:
0.19user 0.06system 0:00.63elapsed 40%CPU (0avgtext+0avgdata 32460maxresident)k
23784inputs+11576outputs (0major+7672minor)pagefaults 0swaps

include/link/object.h

@@ -1,14 +1,30 @@
 /*
  * This file is part of RGBDS.
  *
- * Copyright (c) 1997-2018, Carsten Sorensen and RGBDS contributors.
+ * Copyright (c) 1997-2019, Carsten Sorensen and RGBDS contributors.
  *
  * SPDX-License-Identifier: MIT
  */
 
+/* Declarations related to processing of object (.o) files */
+
 #ifndef RGBDS_LINK_OBJECT_H
 #define RGBDS_LINK_OBJECT_H
 
-void obj_Readfile(char *tzObjectfile);
+/**
+ * Read an object (.o) file, and add its info to the data structures.
+ * @param fileName A path to the object file to be read
+ */
+void obj_ReadFile(char const *fileName);
+
+/**
+ * Perform validation on the object files' contents
+ */
+void obj_DoSanityChecks(void);
+
+/**
+ * `free`s all object memory that was allocated.
+ */
+void obj_Cleanup(void);
 
 #endif /* RGBDS_LINK_OBJECT_H */