Added standard library page, other tweaks

standard-library.md

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+# Standard Library
+
+The standard library offers a number of miscellaneous utility functions, which can be used for various purposes. These functions are implemented by the host program, so they may not all be provided by default.
+
+The standard library can usually be accessed with the `import` keyword:
+
+```
+import standard;
+```
+
+## Clock()
+
+This function returns the current timestamp.
+