Add strz_from_screencode, strz_to_screencode, ENCCONV_SUPPORTED

docs/lang/preprocessor.md

@@ -54,6 +54,8 @@ The following features are defined based on the chosen CPU and compilation optio
 `CPUFEATURE_8080`, `CPUFEATURE_8085`, `CPUFEATURE_GAMEBOY`, `CPUFEATURE_Z80`,
 `CPUFEATURE_6502_ILLEGALS`, `CPUFEATURE_8085_ILLEGALS`, `CPUFEATURE_Z80_ILLEGALS`, `CPUFEATURE_Z80_NEXT` – 1 if given instruction subset is enabled, 0 otherwise
 
+* `ENCCONV_SUPPORTED` - 1 if the module `encconv` supports the function `to_screencode` and other related funtions, 0 otherwise.
+
 * `ENCODING_SAME` - 1 if the encodings `default` and `src` are the same, 0 otherwise.
 
 * `NULLCHAR_SAME` - 1 if the encodings `default` and `src` have the same string terminator, 0 otherwise.

docs/stdlib/encconv.md

@@ -31,6 +31,8 @@ Available only if one of the following is true:
 
 * the default encoding is `atascii`, the screen encoding is `atasciiscr`, and the platform is 6502-based
 
+You can test for the availability of this function using the `ENCCONV_SUPPORTED` preprocessor feature.
+
 #### byte from_screencode(byte)
 
 Converts a byte from the screen encoding to the default encoding.
@@ -39,6 +41,18 @@ If both encodings contain the character `¤`, then `from_screencode('¤'scr) ==
 
 Available only if `to_screencode` is available.
 
+#### void strz_to_screencode(pointer)
+
+Destructively converts a null-terminated string from the `default` encoding into the `scr` encoding. 
+
+Available only if `to_screencode` is available.
+
+#### void strz_from_screencode(pointer)
+
+Destructively converts a null-terminated string from the `scr` encoding into the `default` encoding. 
+
+Available only if `from_screencode` is available.
+
 #### byte petscii_to_petscr(byte)
 
 Converts a byte from PETSCII to a CBM screencode.