ISS-115: Reorganising demo buttons into tabs

[Alphish]

Addressing issue #115

The demos are now divided into categories, and selecting a category in the starting room will show its corresponding demos. This should allow adding more demos for a while, without the starting room getting overcrowded.

[Mercerenies]

Looks good! Now that I've had a chance to run the actual demo, I should note that a couple of the file read/write tests dump some error output to the console. They still pass, so it's not a big deal, but if there's an easy way to get rid of that you might consider it.

ERROR!!! :: Failed to open file: testing/this_file_does_not_exist.txt for buffer_load()
ERROR!!! :: Failed to open file: testing/this_file_does_not_exist.txt for buffer_load()

[Mercerenies]

I learn so many neat GML tricks from reading your code. My way of making pseudo-closures is so much more obnoxiously verbose than this

[Alphish]

I should note that a couple of the file read/write tests dump some error output to the console. They still pass, so it's not a big deal, but if there's an easy way to get rid of that you might consider it.

ERROR!!! :: Failed to open file: testing/this_file_does_not_exist.txt for buffer_load()
ERROR!!! :: Failed to open file: testing/this_file_does_not_exist.txt for buffer_load()

This comes from buffer_load within file_read_all_text
It appears once for testing that file_read_all_text returns undefined for non-available file, and another time for similar json_load test.

I attempt to read a buffer from potentially non-existent file as opposed to checking if file exists beforehand, because:

1. the file might disappear between the check and the loading
2. the file might exist but not be available for other reasons (like, I dunno, security)

Thus, I don't think I can get rid of these messages, if I want to keep the "unable to load buffer for whatever reason" path tested.

Glad the rest of the code looks good to go. ^^

[Mercerenies]

I figured as much. And I agree that preventing the race condition wrt the file existing is more important than getting rid of a rogue line of unit test output. Just thought I'd bring it up in case you weren't aware.