Add source amalgamation

The amalgamated source concatenates all sources
to a file janet.c which can be used for
embedding janet, much in the same way as sqlite
or mongoose.

src/core/corelib.c

@@ -20,10 +20,12 @@
 * IN THE SOFTWARE.
 */
 
+#ifndef JANET_AMALG
 #include <janet/janet.h>
 #include "compile.h"
 #include "state.h"
 #include "util.h"
+#endif
 
 /* Generated bytes */
 extern const unsigned char *janet_gen_core;
@@ -236,7 +238,7 @@ static Janet janet_core_hash(int32_t argc, Janet *argv) {
     return janet_wrap_number(janet_hash(argv[0]));
 }
 
-static const JanetReg cfuns[] = {
+static const JanetReg corelib_cfuns[] = {
     {"native", janet_core_native,
         JDOC("(native path [,env])\n\n"
                 "Load a native module from the given path. The path "
@@ -596,7 +598,7 @@ JanetTable *janet_core_env(void) {
     Janet ret = janet_wrap_table(env);
 
     /* Load main functions */
-    janet_cfuns(env, NULL, cfuns);
+    janet_cfuns(env, NULL, corelib_cfuns);
 
 #ifndef JANET_NO_BOOTSTRAP
     janet_quick_asm(env, JANET_FUN_YIELD, "debug", 0, 1, debug_asm, sizeof(debug_asm),