Add isActive() and isSustain() to envelope

effect_envelope.cpp

 	release(block);
 }
 
+bool AudioEffectEnvelope::isActive()
+{
+	uint8_t current_state = *(volatile uint8_t *)&state;
+	if (current_state == STATE_IDLE) return false;
+	return true;
+}
+
+bool AudioEffectEnvelope::isSustain()
+{
+	uint8_t current_state = *(volatile uint8_t *)&state;
+	if (current_state == STATE_SUSTAIN) return true;
+	return false;
+}
+

effect_envelope.h

 		release_forced_count = milliseconds2count(milliseconds);
 		if (release_count == 0) release_count = 1;
 	}
+	bool isActive();
+	bool isSustain();
 	using AudioStream::release;
 	virtual void update(void);
 private:

gui/index.html

 		disable this feature (never extra latency).  Longer times help
 		reduce clicks or pops.  The default is 5 millisecond.
 	</p>
+	<p class=func><span class=keyword>isActive</span>();</p>
+	<p class=desc>Returns true when the envelope is currently in any of
+		its 6 phases.
+	</p>
+	<p class=func><span class=keyword>isSustain</span>();</p>
+	<p class=desc>Returns true when the envelope is currently in the
+		sustain phase.
+	</p>
 	<h3>Examples</h3>
 	<p class=exam>File &gt; Examples &gt; Audio &gt; Synthesis &gt; PlaySynthMusic
 	</p>

keywords.txt

 sustain	KEYWORD2
 release	KEYWORD2
 releaseNoteOn	KEYWORD2
+isActive	KEYWORD2
+isSustain	KEYWORD2
 inputLevel	KEYWORD2
 inputSelect	KEYWORD2
 muteHeadphone	KEYWORD2