Added README and build script for the Tup-improverished.

README.md

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+# Register Machine Emulator
+
+## What is a register machine?
+
+A register machine is a computing model capable of performing all algorithms possible on modern machines (i.e. it is Turing-complete).
+
+It works by having a finite number of registers, which can store an integer of any length.
+By using a [valid encoding scheme](https://en.wikipedia.org/wiki/G%C3%B6del_numbering), this number can be thought of representing either an instruction, or a value, or a list, or all at once.
+
+## How do you encode programs?
+
+Well, assuming we have a way to encode lists, then we can encode programs as lists of instructions.
+To encode an instruction, we deliberately limit the available number of instructions:
+
+* `0` = `HALT` - stops the program
+* `R+ -> L` - increments register `R`, and subsequently jumps to label `L`
+* `R- -> L1, L2` - decrements register `R` if greater-than `0`, jumping to `L1`. Otherwise (if `R` == `0`), jump to `L2`.
+
+To convert these instructions into numbers, we first convert the instructions into tuples:
+
+* `R+ -> L` ==> <`R`, `L`>
+* `R- -> L1, L2` ==> <`R`, <`L1`, `L2`>>
+
+Here, `R+` instructions are encoded as a pair, and `R-` instructions are encoded as a pair of an integer and a pair.
+
+To distinguish between incrementing and decrementing instructions, we then encode the `R+` instruction register as an even number (2 * `R`).
+And `R-` instructions have an odd-numbered register (2 * `R` + 1).
+
+This all relies on tuples having an encoding, so for further details, see the code.
+
+# Building this emulator.
+
+This requires a working \*nix installation. That should include Linux, the BSDs and MacOS.
+
+Ensure you have [`Tup`](https://github.com/gittup/tup) installed, or use the included `build.sh` script.
+
+You will also require `gcc`, `gmp` and `gmpxx`. `gmpxx` is probably included with `gmp` on your distribution.
+
+## Using `Tup`.
+
+`tup init`
+`tup`
+
+## Using the build script.
+
+`./build.sh`
+
+## Running it.
+
+You should now be able to run the `./Emulator` executable.
+
+Run `./Emulator`, and enter a number at the prompt for a program (no calculation allowed).

build.sh

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+#! /bin/sh -e
+g++  -pedantic -std=c++17 -Wall -Wno-unused-parameter -Wno-reorder -Wno-sign-compare -Wno-address -Wno-noexcept-type -c src/main.cpp -o build/main.o
+g++  -pedantic -std=c++17 -Wall -Wno-unused-parameter -Wno-reorder -Wno-sign-compare -Wno-address -Wno-noexcept-type -c src/register.cpp -o build/register.o
+g++ build/main.o build/register.o  -lgmpxx -lgmp -o Emulator