Add 2 new .ini settings: MainLoopDelay and SocketSelectTimeout (default: 0)

- MainLoopDelay - in milliseconds
  Set this to a non-zero value to add some CPU yielding to the main loop
- SocketSelectTimeout - in milliseconds
  Set this to a non-zero value to add some CPU yielding while waiting for
  receive data from the TCP socket

These are 2 knobs created for Fzf (FQBBS) to "to reduce the CPU usage". Their
default values are currently 0, so you'll need to set these to non-zero values
to play with each of them and see their inpact on CPU utilization and
responsiveness. I'd suggest starting with low values (e.g. 1) and experimeting
from there.

Incremented version to 0.5

src/vdmodem/vdmodem.c

@@ -41,7 +41,7 @@
 #include "git_hash.h"
 
 #define TITLE "Synchronet Virtual DOS Modem for Windows"
-#define VERSION "0.4"
+#define VERSION "0.5"
 
 bool external_socket;
 union xp_sockaddr addr;
@@ -79,6 +79,8 @@ struct {
 	ulong data_rate;
 	bool server_echo;
 	bool server_binary;
+	DWORD main_loop_delay;
+	DWORD socket_select_timeout;
 	char client_file[MAX_PATH + 1];
 	char ip_filter_file[MAX_PATH + 1];
 	char ring_sound[MAX_PATH + 1];
@@ -1105,6 +1107,8 @@ bool read_ini(const char* ini_fname)
 	cfg.server_echo = iniGetBool(ini, ROOT_SECTION, "ServerEcho", cfg.server_echo);
 	cfg.server_binary = iniGetBool(ini, ROOT_SECTION, "ServerBinary", cfg.server_binary);
 	cfg.data_rate = iniGetLongInt(ini, ROOT_SECTION, "Rate", cfg.data_rate);
+	cfg.main_loop_delay = iniGetUInteger(ini, ROOT_SECTION, "MainLoopDelay", cfg.main_loop_delay);
+	cfg.socket_select_timeout = iniGetUInteger(ini, ROOT_SECTION, "SocketSelectTimeout", cfg.socket_select_timeout);
 	cfg.address_family = iniGetEnum(ini, ROOT_SECTION, "AddressFamily", addrFamilyNames, cfg.address_family);
 	char value[INI_MAX_VALUE_LEN];
 	const char* p = iniGetString(ini, ROOT_SECTION, "BusyNotice", NULL, value);
@@ -1389,12 +1393,12 @@ int main(int argc, char** argv)
 	ULONGLONG lastrx = 0;
 	int largest_recv = 0;
 
-	while(WaitForSingleObject(process_info.hProcess,0) != WAIT_OBJECT_0) {
+	while(WaitForSingleObject(process_info.hProcess, cfg.main_loop_delay) != WAIT_OBJECT_0) {
 		ULONGLONG now = xp_timer64();
 		if(modem.online) {
 			fd_set fds = {0};
 			FD_SET(sock, &fds);
-			struct timeval tv = { 0, 0 };
+			struct timeval tv = { 0, cfg.socket_select_timeout * 1000 };
 			result = select(/* ignored: */0, &fds, NULL, NULL, &tv);
 			if(result != 0) {
 				if(result == SOCKET_ERROR)