Read the GSM 03.38 message class where the spec puts it (#95)

* Regression tests for the GSM 03.38 message class behind sms.flash

* Read the GSM 03.38 message class where the spec puts it, and refuse a flash message no alphabet can carry

* Keep the code span in the message-class decision on one line

* Stop offering the flash message class as an alphabet, and check the encoding option by name

* Settle every refusable send option in one check, and record what the review left open

* Say what the flash refusal and the encoding option actually do

* Keep the README off the alphabet whose long messages do not fit

src/message.ts

@@ -51,7 +51,7 @@ export function bitCount(message: string, encoding?: EncodingName): number {
 	const encoded = encodings[resolved].encode(message);
 
 	// GSM characters are packed seven bits to a septet; everything else stays octet-aligned.
-	return resolved === 'ASCII' || resolved === 'FLASH' ? encoded.length * 7 : encoded.length * 8;
+	return resolved === 'ASCII' ? encoded.length * 7 : encoded.length * 8;
 }
 
 /**