v2.4.0: Added visual details to some emojis and revised emojis for better ali…

…gnment with other major emoji sets

We've updated a number of emojis to better align with other emoji
vendor representations, added more detail to some of our earliest
emojis, and cleaned up vector paths for more streamlined SVGs.

This change also moves the Twemoji version number to 2.4.

-- New --

Woman in business suit levitating
Woman in tuxedo

-- Modified --

Angry face with horns
Exploding head
Face with monocle
Face vomiting
Face with stuck-out tongue
Face with stuck-out tongue and winking eye
Face with stuck-out tongue and tightly-closed eyes
Face with rolling eyes
Grinning face with one large and one small eye
Shushing face
Grimacing face
Thinking face
Rolling on the floor laughing
Thumbs up/Thumbs down
Folded Hands
Person gesturing OK
Person with folded hands
Person bouncing ball
Man in Business Suit Levitating
Man in Tuxedo
Man singer
Woman singer
Man office worker
Woman office worker
Families
Brain
Nose
Horse
Pancakes
Birthday cake
Woman's boot
Crossed swords
Crane
Stadium
Tent
Chains
Comet
Sparkles
Rainbow
Roller Coaster
Ferris wheel
Carousel horse
Butterfly
Fountain
Horse racing
Mountain
Snow capped mountain
Mount Fuji
Volcano
Flag in hole
Iran flag
Mauritania flag
Nepal flag
Saudi Arabia flag
Swiss flag
Vatican flag
United Nations flag