modifier buttons for HID mapping + Digital Cstick

[NoShadock]

To play Wind Waker with my N64-usb gamepad, I needed to emulate a CStick.
I chose to map the DPAD to it when a modifier(shift) button is pressed.

Features

Hence this PR adds 2 features:

• Digital CStick: emulate CStick with buttons
• Modifier buttons: up to 3, to combo with other buttons to extend mapping (like ctrl-shift-alt do on a keyboard)

Config changes

For Digital CStick, .ini files have new optional items: DigitalCStick {0 or 1}, and the 8 DPAD directions prepended with 'CStick': 4 standard [CStickUp, CStickRight, CStickDown, CStickLeft], 4 situational(if DPAD=1) [CStickRightUp, CStickDownRight, CStickDownLeft, CStickUpLeft]

For Modifiers, .ini files have 3 new optional items: Mod1, Mod2, Mod3 {button layout}

All button layout are now 3 numbers: Offset, Mask, Modifier#
Modifier# should be 0, 1, 2 or 3 ; otherwise defaulted to 0
When Modifier# is omitted, it is defaulted to 0 which means no modifier.
So it is retro-compatible.

When DigitalCStick=1 ; CStickX, CStickY can still be used for Radius to set the cstick value when buttons are pressed, for instance Radius=50 to get an half-pushed.

Config Example (Generic HID - N64 USB):

[INNEXT N64 USB Gamepad]
VID=0079
PID=0006
Polltype=1
DPAD=1
DigitalCStick=1
DigitalLR=1
Mod1=5,10
A=6,04
B=6,10
X=5,20
Y=5,80
Z=5,40
S=6,20
Power=6,35
L=6,08
R=6,02
StickX=0
StickY=1
Up=5,00
Right=5,02
Down=5,04
Left=5,06
RightUp=5,01
DownRight=5,03
DownLeft=5,05
UpLeft=5,07
CStickUp=5,00,1
CStickRight=5,02,1
CStickDown=5,04,1
CStickLeft=5,06,1
CStickRightUp=5,01,1
CStickDownRight=5,03,1
CStickDownLeft=5,05,1
CStickUpLeft=5,07,1
CStickX=0
CStickY=0