Document 'global' keyword and implicit-global warning

Author: Sainan

docs/New Features/Compiler Warnings.md

@@ -178,6 +178,19 @@ switch a do
 end
 ```
 
+### implicit-global
+This is raised when the `global` keyword is enabled and a global was declared without it. See [Explicit Globals](<Explicit Globals>).
+```pluto showLineNumbers
+pluto_use global
+
+a = 1
+```
+```
+file.pluto:3: warning: implicit global creation [implicit-global]
+    3 | a = 1
+      | ^^^^^ here: prefix this with 'global' if creating a global was intended
+```
+
 ### discarded-return
 This is raised when the return value of a function declared `<nodiscard>` was discarded. See [Nodiscard Functions](<Nodiscard Functions>).
 ```pluto showLineNumbers

docs/New Features/Explicit Globals.md

@@ -0,0 +1,46 @@
+---
+sidebar_position: 2
+---
+
+The optional `global` keyword can be used to explicitly declare global variables.
+
+To enable it, simply do:
+```pluto
+pluto_use global
+```
+
+Then it can be used like this:
+```pluto
+global a = 1
+```
+
+Being identical to the following code:
+```pluto
+a = 1
+```
+
+## Compiler Warnings
+
+When the `global` keyword is enabled, an 'implicit-global' warning is raised for any locals declared without it:
+
+```pluto showLineNumbers
+pluto_use global
+
+a = 1
+```
+```
+file.pluto:3: warning: implicit global creation [implicit-global]
+    3 | a = 1
+      | ^^^^^ here: prefix this with 'global' if creating a global was intended
+```
+
+## `pluto_use` Shorthand
+
+Instead of having to do this:
+```pluto
+pluto_use "0.8.0", global
+```
+You can use a '+' after the version number to not only enable all non-compatible keywords, but also all optional keywords. In this case, the only optional keyword as of Pluto 0.9.0 is `global`, so the above and the following statement are identical:
+```pluto
+pluto_use "0.9.0+"
+```

src/theme/pluto.js

@@ -1,7 +1,7 @@
 Prism.languages.pluto = {
 	'comment': /^#!.+|--(?:\[(=*)\[[\s\S]*?\]\1\]|.*)/m,
 	'attr-name': /(?<=(function|class|extends)\s)[\w:]+/,
-	'keyword': /\$(define\b)?|\b(?:and|as|class|pluto_class|enum|begin|break|do|else|elseif|end|for|goto|if|in|local|new|not|or|repeat|return|static|then|until|while|continue|switch|case|default|pluto_switch|pluto_continue|extends|export|pluto_export|pluto_use|public|private|try|catch|pluto_try|pluto_catch)\b/,
+	'keyword': /\$(define\b)?|\b(?:and|as|class|pluto_class|enum|begin|break|do|else|elseif|end|for|goto|if|in|local|new|not|or|repeat|return|static|then|until|while|continue|switch|case|default|pluto_switch|pluto_continue|extends|export|pluto_export|pluto_use|public|private|try|catch|pluto_try|pluto_catch|global)\b/,
 	'function': [
 		/\b(?!in\s)(?!\d)(?!return)(?!case)(?!function)(?!local)(?!new)\w+(?=\s*(?:\??\())/, // func()
 		/\b(?!in\s)(?!\d)(?!return)(?!case)(?!function)(?!local)(?!not)\w+(?=\s*(?:\??[{"]))/, // func "", func {}