Add shell.c to the amalgamation.

This allows easy builds of the full interpreter with no
build system.

  1. Get janet.c, janet.h, janetconf.h, and shell.c in a directory. Edit
     janetconf.h as desired.
  2. gcc shell.c janet.c -lm -ldl -O2 -o janet (on GNU-Linux for example)
  3. ./janet -h (Yay!)

src/mainclient/line.c

@@ -20,7 +20,9 @@
 * IN THE SOFTWARE.
 */
 
+#ifndef JANET_AMALG
 #include "line.h"
+#endif
 
 /* Common */
 Janet janet_line_getter(int32_t argc, Janet *argv) {

src/mainclient/line.h

@@ -23,7 +23,9 @@
 #ifndef JANET_LINE_H_defined
 #define JANET_LINE_H_defined
 
+#ifndef JANET_AMALG
 #include <janet.h>
+#endif
 
 void janet_line_init();
 void janet_line_deinit();

src/mainclient/main.c

@@ -20,8 +20,10 @@
 * IN THE SOFTWARE.
 */
 
+#ifndef JANET_AMALG
 #include <janet.h>
 #include "line.h"
+#endif
 
 #ifdef _WIN32
 #include <windows.h>