Support Unicode Symbols

[ronkok]

This is the third in a series of PRs to give KaTeX the ability to recognize Unicode character input. This one supports some but not all letter-like symbols and some other symbols. All the characters in this PR will produce textord atoms in math mode.

The list is not comprehensive. It’s a bit eclectic. Some of these characters are important. Others were just easy to include. A few important characters are omitted because it wasn’t clear to me which is the best way to implement them. I’ll address those characters in future PRs.

[ronkok]

Double-struck characters cannot be done with current fonts by just setting a flag in symbols.js. Take ℂ, for example. In the katex-ams font, the character that looks like ℂ is not at code point U+2102 but is instead at code point U+0043. So, the symbols.js flag technique doesn’t work. Rather than wait for font revisions, I wrote macros.

[ronkok]

As in PR #933, the following table shows the KaTeX function to which each character is mapped and confirmation whether unicode math and/or John Cook’s conversion page map it the same way.

Character	Code point	Maps to	unicode math	Cook	Other
£	U+00A3	\pounds	\mathsterling	\sterling	\textsterling
¥	U+00A5	\yen	\mathyen	✓
ð	U+00F0	\eth	\matheth	\dh
ℂ	U+2102	\mathbb{C}	\BbbC	\BbbC
ℍ	U+210D	\mathbb{H}	\BbbH	\BbbH
ℑ	U+2111	\Im	✓	✓	\frakI
ℓ	U+2113	\ell	✓	✓
ℕ	U+2115	\mathbb{N}	\BbbN	\BbbN
℘	U+2118	\wp	✓	✓
ℙ	U+2119	\mathbb{P}	\BbbP	\BbbP
ℚ	U+211A	\mathbb{Q}	\BbbQ	\BbbQ
ℜ	U+211C	\Re	✓	✓	\frakR
ℝ	U+211D	\mathbb{R}	\BbbR	\BbbR
ℤ	U+2124	\mathbb{Z}	\BbbZ	\BbbZ
Ⅎ	U+2132	\Finv	✓	✓
ℵ	U+2135	\aleph	✓	✓
ℶ	U+2136	\beth	✓	✓
ℷ	U+2137	\gimel	✓	✓
ℸ	U+2138	\daleth	✓	✓
⅁	U+2141	\Game	✓	✓
∀	U+2200	\forall	✓	✓
∁	U+2201	\complement	✓	✓
∂	U+2202	\partial	✓	✓
∃	U+2203	\exists	✓	✓
∇	U+2207	\nabla	✓	✓	\del
∞	U+221E	\infty	✓	✓
∠	U+2220	\angle	✓	✓
∡	U+2221	\measuredangle	✓	✓
∢	U+2222	\sphericalangle	✓	\sphericalangle \ltrpar
♠	U+2660	\spadesuit	✓	✓
♡	U+2661	\heartsuit	✓	✓
♢	U+2662	\diamondsuit	✓	✓
♣	U+2663	\clubsuit	✓	✓
♭	U+266D	\flat	✓	✓
♮	U+266E	\natural	✓	✓
♯	U+266F	\sharp	✓	✓
✓	U+2713	\checkmark	✓	✓

[kevinbarabash]

Rather than wait for font revisions, I wrote macros.

I think that's sensible. I think revising the fonts would introduce other complications as it relates to handling font commands such as \mathbb, etc.

[ronkok]

Let's hold off on this until after PR #973 lands. I'll revise this PR accordingly.

[ronkok]

The most recent commit reverts a RegEx in MacroExpander.js. So the code in this PR is now dependent on PR #973.

[ronkok]

Now that PR #973 has landed, this should be good to go.

[kevinbarabash]

LGTM

[kevinbarabash]

nice!