feat(CI): add a GitHub Action to check spelling

- Fix spelling
- Run only on pull request
- Using https://github.com/client9/misspell

.github/workflows/spell-checker.yml

+name: 💎 Spellchecker
+
+on: [pull_request]
+
+jobs:
+  misspell:
+    name: 🧹 Check Spelling
+    runs-on: ubuntu-latest
+    steps:
+      - name: 🍒 Check Out
+        uses: actions/checkout@v2
+      - name: 🍅 Install
+        run: |
+          wget -O - -q https://git.io/misspell | sh -s -- -b .
+      - name: 🌶️ Misspell
+        run: |
+          find . -type f | xargs ./misspell -error

mrbgems/mruby-compiler/core/codegen.c

@@ -856,7 +856,7 @@ lambda_body(codegen_scope *s, node *tree, int blk)
     oa = node_len(tree->car->cdr->car);
     /* rest argument? */
     ra = tree->car->cdr->cdr->car ? 1 : 0;
-    /* mandatory arugments after rest argument */
+    /* mandatory arguments after rest argument */
     pa = node_len(tree->car->cdr->cdr->cdr->car);
     pargs = tree->car->cdr->cdr->cdr->car;
     /* keyword arguments */

mrbgems/mruby-compiler/core/parse.y

@@ -6826,7 +6826,7 @@ str_dump(mrb_state *mrb, const char *str, int len)
   int ai = mrb_gc_arena_save(mrb);
   mrb_value s;
 # if INT_MAX > MRB_INT_MAX / 4
-  /* check maximum length with "\xNN" charactor */
+  /* check maximum length with "\xNN" character */
   if (len > MRB_INT_MAX / 4) {
     len = MRB_INT_MAX / 4;
   }

mrbgems/mruby-compiler/core/y.tab.c

@@ -12827,7 +12827,7 @@ str_dump(mrb_state *mrb, const char *str, int len)
   int ai = mrb_gc_arena_save(mrb);
   mrb_value s;
 # if INT_MAX > MRB_INT_MAX / 4
-  /* check maximum length with "\xNN" charactor */
+  /* check maximum length with "\xNN" character */
   if (len > MRB_INT_MAX / 4) {
     len = MRB_INT_MAX / 4;
   }

mrbgems/mruby-io/src/file.c

@@ -298,7 +298,7 @@ is_absolute_traditional_path(const char *path, size_t len)
 }
 
 static int
-is_aboslute_unc_path(const char *path, size_t len) {
+is_absolute_unc_path(const char *path, size_t len) {
   if (len < 2) return 0;
   return (CHECK_UNCDEV_PATH && !IS_DEVICEID(path[2]));
 }
@@ -317,7 +317,7 @@ mrb_file_is_absolute_path(const char *path)
   if (len > 0)
     return (
       is_absolute_traditional_path(path, len) ||
-      is_aboslute_unc_path(path, len) ||
+      is_absolute_unc_path(path, len) ||
       is_absolute_device_path(path, len)
       );
   else