add SC7A20 ACCELEROMETER SENSOR

Author: shaoziyang

sensor/SC7A20/READMD.md

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+# [mpy-lib](https://github.com/micropython-Chinese-Community/mpy-lib)
+
+## SC7A20 3-AXIS ACCELEROMETER SENSOR 
+
+<img width = '200' height ='165' src ="https://www.silan.com.cn/en/upload/2020/03/31/1585637043217ivfnz.png">
+
+- https://www.silan.com.cn/en/index.php/product/details/47.html
+
+The SC7A20 is an acceleration sensor IC, which features abundant functions, low power dissipation, small size, and precision measurement.
+
+## Example
+
+
+```py
+from machine import I2C, Pin
+from time import sleep_ms
+
+from SC7A20 import SC7A20
+
+i2c = I2C(0, sda=Pin(4), scl=Pin(16))
+
+sc = SC7A20(i2c)
+
+while True:
+    print(sc.x(), sc.y(), sc.z())
+    sleep_ms(100)
+```

sensor/SC7A20/SC7A20.py

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+from machine import I2C
+
+class SC7A20:
+    
+    def __init__(self, i2c, SDO = 1):
+        self.i2c = i2c
+        self.ADDR = 0x19 if SDO == 1 else 0x18
+        self._ODR = 4
+        self._LPen = 1
+        self._FS = 0
+        self._HR = 1
+        self.tb = bytearray(1)
+        self.rb = bytearray(1)
+        self.init()
+        
+    def reg_set(self, reg, val):
+        self.tb[0] = val
+        self.i2c.writeto_mem(self.ADDR, reg, self.tb)
+        
+    def reg_get(self, reg):
+        self.i2c.readfrom_mem_into(self.ADDR, reg, self.rb)
+        return self.rb[0]
+        
+    def rw_reg(self, reg, dat, mask):
+        self.reg_get(reg)
+        self.rb[0] = (self.rb[0] & mask) | dat
+        self.reg_set(reg, self.rb[0])
+        
+    def ODR(self, odr = None):
+        if odr != None:
+            self._ODR = odr
+            self.rw_reg(0x20, odr<<4, 0x0F)
+        else:
+            return self._ODR
+    
+    def LP(self, lp = None):
+        if lp != None:
+            self._LPen = lp
+            self.rw_reg(0x20, lp<<3, 0x08)        
+        else:
+            return self._LPen
+    
+    def FS(self, fs = None):
+        if fs != None:
+            self._FS = fs
+            self.rw_reg(0x23, fs<<4, 0xCF) 
+        else:
+            return self._FS
+ 
+    def HR(self, hr = None):
+        if hr != None:
+            self._HR = hr
+            self.rw_reg(0x23, hr<<3, 0x08) 
+        else:
+            return self._HR
+        
+    def on(self):
+        self.ODR(self._ODR)
+        
+    def off(self):
+        self.ODR(0)
+    
+    def init(self):
+        # enable TEMP
+        self.reg_set(0x1F, 255)
+        # ODR 4 (50Hz), LPEN = 1, XYZen = 1
+        self.LP(1)
+        # BDU = BLE = 0, FS = 0 (2G), HR = 1
+        self.FS(0)
+        self.HR(1)
+        self.on()
+        # int lock
+        self.reg_set(0x24, 0x0F)
+
+    def int16(self, d):
+        return d if d < 0x8000 else d - 0x10000
+
+    def T(self):
+        return self.reg_get(0x0D)
+        
+    def rawx(self):
+        return self.reg_get(0x28) + self.reg_get(0x29)*256
+        
+    def rawy(self):
+        return self.reg_get(0x2A) + self.reg_get(0x2B)*256
+        
+    def rawz(self):
+        return self.reg_get(0x2C) + self.reg_get(0x2D)*256
+
+    def x(self):
+        return self.int16(self.rawx())>>(4-self._FS)
+
+    def y(self):
+        return self.int16(self.rawy())>>(4-self._FS)
+
+    def z(self):
+        return self.int16(self.rawz())>>(4-self._FS)
+
+    
+