Simplify the language and start building a parse tree

We now only support expressions that are ints or sums thereof.
Initial assembly generation!
Sol is a pussywillow.
Freed up registers and fixed bool include.
Syntax errors cause abortion!
Write helper script for making object files from compiler output
Actually pass "final" program result to the putint() function

Whatever's in %eax ... doesn't stay in %eax. To be exact, it gets
printed.
More complete shit.
Added symbol memory prototypes.
Start implementing symbol_memory module

This will be responsible for actually managing the scratch registers,
stack (or maybe heap?) memory, and shuffling values between them (as
well as providing assembly language names for the registers, which will
be used by client code during tree traversal/code generation).
This is still unfinished work at this point, what with memory-related
decisions needing to be made within this module, and et_compiler
requiring some weaning off the old SCRATCH_REGS paradigm.
Jot down a couple of memory ideas that may or may not prove useful
Start reimplementing code generation to use new symbol module

Most of the credit for this goes to Jos. A lot of cases are still
missing, and it cannot yet be tested because significant pieces of the
symbol module are actually missing!
Added new operands and ignores spaces and tabs.
Implement---but don't actually test whatsoever---the much-dreaded symbol_request_reg()

This is going to be a doozy!
Assertion `safe_and_sound' failed

Or, "How I plumbed that final, missing piece, only to have the rush of
instant gratification immediately subdued by the realization that our
hero, symbol_request_reg(), is actually broken."
Fix bug where symbol_add() updated the register_table but failed to add a cross-reference from symbol_table
Actually populate the out_registers out parameter of symbol_give_me_my_stuff()

This fixes an issue where register names couldn't actually be printed.
Free up last symbol if final operation is indirect.
Implemented binary operators with direct, then indirect.
Indirect, direct, all seems to work wooooooooooo but we need to test