Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

include/ttf.h

@@ -0,0 +1,49 @@
+#pragma once
+
+// TrueType outlines, as a font provider for include/text.h.
+//
+// Scope, and why it is this and not "TTF and OTF":
+//
+// .ttf and .otf are both sfnt containers -- the same table directory, the same
+// cmap, the same hmtx. What differs is how outlines are stored. TrueType puts
+// quadratic B-spline contours in a `glyf` table; OpenType/PostScript puts cubic
+// béziers in a `CFF ` table encoded as Type 2 charstrings, which is a
+// stack-based interpreted format and a separate project.
+//
+// Checked before writing any of it: JetBrains Mono and Roboto -- the two fonts
+// this system is going to use -- both ship `glyf` and neither ships `CFF `. So
+// CFF support would buy nothing today, and the honest thing is to implement the
+// format the fonts actually use and say so, rather than half-implement two.
+//
+// Everything here is from Apple's TrueType Reference Manual and the OpenType
+// specification, both public documents.
+
+struct ttf {
+  const unsigned char *data;
+  uint32 len;
+
+  uint32 glyf, glyf_len;
+  uint32 loca, loca_len;
+  uint32 cmap4;               // offset of the format 4 subtable, 0 if none
+  uint32 hmtx;
+  int    num_glyphs;
+  int    num_hmetrics;
+  int    units_per_em;
+  int    long_loca;           // indexToLocFormat: 0 = 16-bit offsets, 1 = 32
+  int    ascent, descent;
+
+  // Rasterisation target size, in pixels per em. Set by ttf_open.
+  int    px;
+};
+
+// Parse a font already in memory. Returns 0, or -1 if it is not a TrueType
+// font this can read. `data` must outlive the struct -- nothing is copied.
+int ttf_open(struct ttf *, const void *data, uint32 len, int pixels_per_em);
+
+// Rasterise one codepoint into `cov`. Returns 0, or -1 if the font has no such
+// glyph or it will not fit. Exposed because the host harness uses it directly.
+int ttf_render(struct ttf *, uint32 cp, struct glyph *out, unsigned char *cov,
+               int covcap, int *ox, int *oy);
+
+// A font provider over it, for text.h. The struct must outlive the font.
+struct font *ttf_font(struct ttf *);