Documentation fixes

docs/stdlib/stdio.md

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+[< back to index](../index.md)
+
+## stdio
+
+The `stdio` module automatically imports the `string` and `err` modules.  
+It requires an implementation of `void putchar(byte a)` and therefore works only on targets with console output.
+
+#### `void putstr(pointer str, byte len)`
+
+Prints a string of length `len` located at address `str`.  
+
+#### `void putstrz(pointer str)`
+
+Prints a null-terminated string located at address `str`.  
+If the string is longer than 255 bytes, then the behaviour is undefined (might even crash).
+
+#### `void putword(word w)`
+
+Prints the decimal representation of the 16-bit unsigned integer `w`.
+
+#### `void ensure_mixedcase()`
+
+On targets that have separate all-caps and mixed-case modes (like most Commodore machines), switches to the mixed-case mode.
+