Modernize docs

[DiscoStarslayer]

Initial attempt at cleaning up the docs a bit.

Markdown is more standard and a little easier to read, also lets you skip a changelog to figure out how to use it.

See proposed readme formatted here

Closes #1

[JayFoxRox]

Left some more nits to turn this bikeshed into a luxury bike resort.

I proof-read the document and think it's fine. Thanks for spending the time to writing it initially, and the continuous improvements!

So the only thing left to do before merge (from what I see): Fix the one non-nit review comment (which is confusing), then squash-up into a single commit and adopt commit title style of previous commit ("docs: Modernize README using markdown" or something along those lines).

[GXTX]

I still think the docs are very cluttered after this PR but it's a lot better than the old change log.

Here's a "build guide" for MSYS on Windows.

pacman -S git make mingw-w64-x86_64-cmake mingw-w64-x86_64-gcc
git clone https://github.com/XboxDev/extract-xiso
cd extract-xiso && mkdir build && cd build
cmake .. -G "MSYS Makefiles"
make

[mborgerson]

Version information is stale. We should probably add a step that integrates the Git commit-id somehow. [Not an issue with this PR, but still something to be aware of]

[JayFoxRox]

Has nothing to do with this PR though.

Create an issue or PR please.

[DiscoStarslayer]

Great catch, also agree it is out of scope for this PR. Created an issue to capture @mborgerson's findings: #21

[mborgerson]

Thanks @DiscoStarslayer !