Support reading legacy sendprop arrays (#1550)

This rounds out the work started in #1548 to complete support for
reading the older SendPropArray type array netprops, along with bringing
SDKTools' GameRule netprop code in sync with core to add string array
support.

There aren't many SendPropArray type props around but this opens up a
few interesting opportunities for plugin developers, particularly in
L4D2 with manipulation of the EMS HUD.

Tested reading the `m_vCPPositions` array in TF2, and reading/writing
the `m_szScriptedHUDStringSet` EMS HUD netprop in L4D2. Closes #1386.

plugins/include/sdktools_gamerules.inc

@@ -169,10 +169,11 @@ native void GameRules_SetPropVector(const char[] prop, const float vec[3], int e
  * @param prop          Property to use.
  * @param buffer        Destination string buffer.
  * @param maxlen        Maximum length of output string buffer.
+ * @param element       Element # (starting from 0) if property is an array.
  * @return              Number of non-null bytes written.
  * @error               Prop type is not a string, or lack of mod support.
  */
-native int GameRules_GetPropString(const char[] prop, char[] buffer, int maxlen);
+native int GameRules_GetPropString(const char[] prop, char[] buffer, int maxlen, int element=0);
 
 /**
  * Sets a gamerules property as a string.
@@ -180,10 +181,11 @@ native int GameRules_GetPropString(const char[] prop, char[] buffer, int maxlen)
  * @param prop          Property to use.
  * @param buffer        String to set.
  * @param changeState   This parameter is ignored.
+ * @param element       Element # (starting from 0) if property is an array.
  * @return              Number of non-null bytes written.
  * @error               Prop type is not a string, or lack of mod support.
  */
-native int GameRules_SetPropString(const char[] prop, const char[] buffer, bool changeState=false);
+native int GameRules_SetPropString(const char[] prop, const char[] buffer, bool changeState=false, int element=0);
 
 /**
  * Gets the current round state.