Add a `dist` rule to the Makefile
Add a `dist` rule to the Makefile

Summary: Adds a `dist` rule to the Makefile which builds the `dist/`
directory with all of the built files in it.

Test plan:
 - `make dist`

Auditors: alpert

crepererum/KaTeX,franciscop/KaTeX,zhanghuiguoanlige/KaTeX,mcanthony/KaTeX,frankandrobot/KaTeX,kwangkim/KaTeX,crepererum/KaTeX,kevinbarabash/KaTeX,frankandrobot/KaTeX,spicyj/KaTeX,kwangkim/KaTeX,xymostech/KaTeX,twitwi/KaTeX,spicyj/KaTeX,saschatimme/KaTeX,crepererum/KaTeX,kwangkim/katex-npm-0.7.0-pre,twitwi/KaTeX,JetStarBlues/KaTeX,azotova/KaTeX,xymostech/KaTeX,kevinbarabash/KaTeX,saschatimme/KaTeX,twitwi/KaTeX,kwangkim/KaTeX,gagern/KaTeX,zhanghuiguoanlige/KaTeX,zhanghuiguoanlige/KaTeX,crepererum/KaTeX,JetStarBlues/KaTeX,frankandrobot/KaTeX,Khan/KaTeX,kwangkim/katex-npm-0.7.0-pre,spicyj/KaTeX,gagern/KaTeX,Khan/KaTeX,xymostech/KaTeX,kevinbarabash/KaTeX,mcanthony/KaTeX,azotova/KaTeX,gagern/KaTeX,mcanthony/KaTeX,kwangkim/KaTeX,spicyj/KaTeX,JetStarBlues/KaTeX,gagern/KaTeX,kevinbarabash/KaTeX,frankandrobot/KaTeX,kwangkim/katex-npm-0.7.0-pre,xymostech/KaTeX,franciscop/KaTeX,crepererum/KaTeX,JetStarBlues/KaTeX,azotova/KaTeX,xymostech/KaTeX,twitwi/KaTeX,kwangkim/katex-npm-0.7.0-pre,franciscop/KaTeX,saschatimme/KaTeX,saschatimme/KaTeX,zhanghuiguoanlige/KaTeX,franciscop/KaTeX,gagern/KaTeX,twitwi/KaTeX,franciscop/KaTeX,JetStarBlues/KaTeX,Khan/KaTeX,kwangkim/katex-npm-0.7.0-pre,spicyj/KaTeX,zhanghuiguoanlige/KaTeX,kwangkim/KaTeX,saschatimme/KaTeX,mcanthony/KaTeX,azotova/KaTeX,mcanthony/KaTeX,frankandrobot/KaTeX,kevinbarabash/KaTeX,azotova/KaTeX