Use less confusing language for compiled and decompiled tilesets, see description

[grunt-lucas]

In order to be more clear:

Compiled tilesets should be referred to as "Porymap-format tilesets"

Decompiled tilesets should be referred to as "Porytiles-format tilesets".

Thus, the compiler takes you from a Porytiles-format tileset to a Porymap-format tileset. And the decompiler takes you from a Porymap-format tileset to a Porytiles-format tileset.

We can have documentation that officially defines a Porymap-format tileset and a Porytiles-format tileset.

Let's refactor the code to use these names as well.