Add provides key to some languages

Provides key allows 1 package to provide multiple languages

Expect an API update to work with these new packages

packages/gcc/10.2.0/compile

@@ -3,21 +3,21 @@
 # Put instructions to compile source code, remove this file if the language does not require this stage
 
 
-case "${PISTON_ALIAS}" in
-    gcc | c)
+case "${PISTON_LANGUAGE}" in
+    c)
         rename 's/$/\.c/' "$@" # Add .c extension
         gcc -std=c11 *.c -lm
         ;;
-    g++ | c++ | cpp)
+    c++)
         rename 's/$/\.cpp/' "$@" # Add .cpp extension
         g++ -std=c++17 *.cpp
         ;;
-    gdc | d)
+    d)
         rename 's/$/\.d/' "$@" # Add .d extension
         gdc *.d
         ;;
     *)
-        echo "How did you get here? (${PISTON_ALIAS})"
+        echo "How did you get here? (${PISTON_LANGUAGE})"
         exit 1
         ;;
 esac

packages/gcc/10.2.0/metadata.json

@@ -1,5 +1,18 @@
 {
     "language": "gcc",
     "version": "10.2.0",
-    "aliases": ["c", "g++", "c++", "cpp", "gdc", "d"]
+    "provides": [
+        {
+            "language":"c",
+            "aliases": ["gcc"]
+        },
+        {
+            "language": "c++",
+            "aliases": ["cpp", "g++"]
+        },
+        {
+            "language": "d",
+            "aliases": ["gdc"]
+        }
+    ]
 }