Create Formicid species and monsters.

Tavern post:
https://crawl.develz.org/tavern/viewtopic.php?f=8&t=8298

Wierdness & mutations:
- poison weakness
- retractable antennae (can wear headgear and ignore mutation)
- chitin skin (+3 AC)
- most weapons 1-handed, big weapons 2-handed
- permanent stasis
- ability to shaft self
- ability to dig
- Starts with 2 curing pots

3 monster versions of formicids were added:
formicid, a weak fighter
formicid drone, a stronger fighter
formicid venom mage, a magician with olgreb's and mass cure poison

[ Pushing to a branch for experimental playtesting on CSZO.
  Also optimised the new tiles. -nfm ]
Increase digging loudness.
Lessen the noise of self-shaft.
Mention that shafting takes turns when being used.

It wasn't obvious enough, and the message had room in the prompt.
Mention that Formicids can wield 2h with shield.

It wasn't obvious without reading the manual.
The new message isn't perfect, but should prompt players to look into
the 2h + shield deal better.
Imporve formicid ability descriptions.

Digging needed a mention of the noise.

Shafting needed mention of the turn delay and landing noise.
Give SPELL_DIG to orc sorcerers.

It was brought up that formicid's infinite digging was problematic on
orc:4, as you could easily break los with a bent tunnel.
By giving orc sorcerers the dig spell, it makes formicid digging less
effective.

Obviously sorcerers didn't need this spell before, and if this addition
negatively affects the game then it should be removed later.
Add a formicid monster vault.

The vault's weight is set very high for purposes of testing.

The depth may be wrong for the difficulty.
Add some placeholder formicid tiles.

Since all 3 formicid monsters appear together they needed tiles to
separate them.
These are absolutely terrible graphics, but should suffice for testing purposes.
Remove the delay of formicids removing helmet.

The delay remains for wearing helmets, but it was redundant to have it
also happen when removing.
Display message when removing helmets as Formicid.

It isn't obvious that your antennae extend slowly on console.
Mention that shafting changes OOD timer.
Tweak formicid aptitudes.

Lessened armour and shields by one as their defences were too high.
Set tloc to -1 because it makes sense flavor-wise.
Fix whitespace.
Replace chitin skin mutation with exoskeleton.

Exoskeleton provides HP +5, AC +1. This is to make the game easier in
the beginning.
Negate swiftness with stasis.

Negating swiftness is an important design choice of Formicids.
Unfortunately, the stasis amulet will suffer slightly, although it is a
very uncommon effect.
Replace Formicid mon flags with genus checks.

There's no point in taking up flag space when genus checks work fine.
Improve formicid monster gear.

They now get shields and their weapon variety is improved slightly.
Add new formicid vault and improve old one.

The new vault is much easier and can go in lair.
The old one was moved to an earlier depth.
Both weights were set to the default value.
Make dig carve-out more adjacent tiles to player.

This is a nerf to prevent players from digging twice to break LOS.
While it's still possible to create single tile corridors, you won't be
able to use digging to completely block LOS.