feat(macro): improve argument parsing (#2085)

* Improve macro argument parsing

* Make \above a primitive command

* Fix screenshotter data

* Normalize argument where necessary

* Improve argument location info

* Update comments

* Minor refactor

* Modularize group parsers

* Allow braced and blank size argument

for non-strict mode and \genfrac, respectively.

* Minor refactor & update comments

* Remove raw option in parseStringGroup

* Update tests

* Fix { delimited parameter

* Update tests

* Update tests

* Normalize argument in \genfrac

* Update tests

* Consume space before scanning an optional argument

* Fix \\, \newline, and \cr behavior

* Fix flow error

* Update comments

* Remove unnecessary mode switching

Parser mode affects neither fetch nor consume.

* Allow single (active) character macro

* Add function property `primitive`

* Set \mathchoice and \*style primitive

* Separate size-related improvements out to #2139

* Fix flow error

* Update screenshots

* Update demo example

* Add a migration guide

* Fix capitalization

* Make a primitive function unexpandable

* Update screenshots

* Update screenshots

* Revert "Document \def doesn't support delimiters (#2288) (#2289)"

This reverts commit f96fba6f7f.

* Update comments, errors, and tests

* Update screenshots

website/pages/index.html

@@ -62,9 +62,9 @@
             </a>
           </div>
           <textarea id="demo-input" spellcheck="false">
-% \f is defined as f(#1) using the macro
-\f{x} = \int_{-\infty}^\infty
-    \hat \f\xi\,e^{2 \pi i \xi x}
+% \f is defined as #1f(#2) using the macro
+\f\relax{x} = \int_{-\infty}^\infty
+    \f\hat\xi,e^{2 \pi i \xi x}
     \,d\xi</textarea>
         </div>
         <div class="demo-right">
@@ -181,7 +181,7 @@
       <h4><label for="macros">macros</label></h4>
       <textarea id="macros" placeholder="JSON">
 {
-    "\\f": "f(#1)"
+    "\\f": "#1f(#2)"
 }</textarea>
 
       <h3>Editor Options</h3>

website/sidebars.json

@@ -3,6 +3,6 @@
     "Installation": ["node", "browser"],
     "Usage": ["api", "cli", "autorender", "libs"],
     "Configuring KaTeX": ["options", "security", "error", "font"],
-    "Misc": ["supported", "support_table", "issues"]
+    "Misc": ["supported", "support_table", "issues", "migration"]
   }
 }