Add full compiler toolchain, libc, examples and reference docs

First substantive commit: the entire Sprinter C compiler tree on top of
the bare README+gitignore initial commit.

What's in here:
  bin/sprinter-cc        — driver script invoking SDCC + linker + mkexe
  libc/                  — Sprinter-specific libc layer over ESTEX/BIOS
                           (conio, gfx, io, mem, stdio + headers)
  runtime/               — crt0 variants (default/small/banked/minimal)
                           + heap + bank trampolines
  toolchain/             — mkexe (SprintEXE packer, C + tests)
  examples/              — 30 demo programs (gfx, file I/O, env, time, …)
  lib/Makefile           — builds the libc archive (sprinter.lib)
  docs/                  — converted Sprinter manuals + asm reference samples
  third_party/           — solid-c reference compiler dump + sdcc setup script
  release_docs/          — packaging / release notes

gitignore overhaul:
  • Drop dangerous blanket patterns: *.asm (would hide docs/samples/*.asm)
    and *.exe (case-insensitive match was hiding third_party/solid-c/*.EXE
    on macOS APFS).  Replaced with examples/*/*.{asm,exe,…} and lib/*.lib.
  • Restore tracking of toolchain/mkexe/tests/{one,big}.bin — those are
    INPUT fixtures, not build outputs.
  • Collapse the duplicated SDCC/C/Sdcc sections into one section per
    concern (build outputs / vendored / OS-junk).
  • Add .sprinter-cc-*/, build/ (catches lib/build/ too), .claude/.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

third_party/solid-c/INCLUDE/DOS.H

@@ -0,0 +1,100 @@
+/*
+ *	DOS.H
+ *
+ *	Defines structs, unions, and functions for
+ *	dealing with Estex-DOS.
+ *	(c) 2004, SOLID C  Sprinter-2000
+ */
+
+
+#ifndef	_C_TYPES_
+#include <types.h>
+#endif
+
+
+/* Variables */
+extern int _argc;
+extern char **_argv;
+
+
+/* DOS types */
+struct WORDREGS {
+    unsigned af, bc, de, hl, ix, iy;
+};
+
+struct BYTEREGS {
+    char flag, a, c, b, e, d, l, h;
+};
+
+union REGS {
+    struct WORDREGS x;
+    struct BYTEREGS h;
+};
+
+
+struct time {
+    unsigned char  ti_min;	/* minutes */
+    unsigned char  ti_hour;	/* hours */
+    unsigned char  ti_hund;	/* hundredths of seconds. Not used. */
+    unsigned char  ti_sec;	/* seconds */
+};
+
+struct date {
+    int  da_year;		/* year */
+    char da_day;		/* day of the month */
+    char da_mon;		/* month (1 = Jan) */
+};
+
+
+/* ffirst, fnext functions */
+typedef struct ffblk {
+    char name[8];		/* +0  pattern of a file name */
+    char ext[3];		/* +8  pattern of file expansion */
+    char attrib;		/* +11 search attribute */
+    char ff_resv[10];		/* +12 reserved for DOS */
+    uint ff_time;		/* +22 time of last write to file */
+    uint ff_date;		/* +24 date of last write to file */
+    uint ff_clst;		/* +26 number of first cluster */
+    uint ff_lsize;		/* +28 low size of file */
+    uint ff_hsize;		/* +30 high size of file */
+    char ff_attr;		/* +32 attribute byte of matched file */
+    char ff_name[223];		/* +33 null-terminated name of matched file */
+} FIND;
+
+
+/* file attributes */
+#define FA_NORMAL   0x00	/* Normal file, no attributes */
+#define FA_RDONLY   0x01	/* Read only attribute */
+#define FA_HIDDEN   0x02	/* Hidden file */
+#define FA_SYSTEM   0x04	/* System file */
+#define FA_LABEL    0x08	/* Volume label */
+#define FA_DIREC    0x10	/* Directory */
+#define FA_ARCH     0x20	/* Archive */
+
+
+
+
+/* Prototypes */
+
+char bdos();			/* DOS call return status */
+int  bdosh();			/* DOS call return int */
+void intdos();			/* DOS call, parameters and return as REGS */
+void enable();			/* enable interrupts */
+void disable();			/* disable interrupts */
+char absread();			/* read sectors */
+char abswrite();		/* write sectors */
+char ffirst();			/* found first file */
+char _ffirst();			/* found first file, format "FilenameExt" */
+char fnext();			/* found next file */
+int _setargv();			/* parsing arguments */
+void setdisk();			/* set default disk */
+char getdisk();			/* get default disk */
+void setdate();			/* set system date */
+void getdate();			/* get struct date */
+void settime();			/* set system time */
+void gettime();			/* get struct time */
+void sleep();
+
+
+#define findfirst  ffirst
+#define findnext   fnext