Alchemist TD - new campaign system, achievements, and more gems

I wanted to wait with this update until the game is developed to such a degree, that it will be fun not only for playing a single map, but for a whole campaign.

With the overworld map screen and the ability to unlock gem combinations that is achieved now.

New features:

- Basic gems can be combined into crystals which are similar to special gems but weaker.

- Initially, special gems are locked. These can be unlocked by spending 5 experience.

- Experience is gained by completing maps. 

- Added desert and snow maps, these are different only visually.

- Each map has a set of enemies that appear there.

- The next 5 incoming enemy waves are displayed in the bottom right corner.

Clicking this you can check the enemy unit stats.

- Complete achievements for extra experience rewards.

- Lots of sound effects.

As always, comments and suggestions are welcome. I am especially looking for new achievement ideas.

Here is link where you can play Alchemist:

https://lizardwizard.itch.io/alchemisttd