Ely Office: six offline-first desktop apps in Rust and GPUI

ElyDoc, ElyTable, ElyShow (LibreOfficeKit), ElyPDF (MuPDF), ElyTree (Git),
ElyMark (Milkdown and CodeMirror in CEF). ElyMail and ElyAgent follow.

tests/fixtures/mark/extended.md

@@ -0,0 +1,36 @@
+# Title
+
+Text with $e^{i\pi} + 1 = 0$ inline and a note.[^1]
+
+$$I = \int \rho R^{2} dV$$
+
+- [x] done
+- [ ] open
+
+| a | b |
+| - | - |
+| 1 | 2 |
+
+```rust
+fn main() {}
+```
+
+$$
+\int_0^1 x\,dx
+$$
+
+$$
+\frac{1}{
+$$
+
+```mermaid
+graph TD
+  A --> B
+```
+
+```mermaid
+graph TD
+  A -->
+```
+
+[^1]: The note.