add SHT3x drive

SHT3x humidity and temperature sensor 8bit I2C micropython drive

Author: shaoziyang

sensor/SHT3x/I2C_8bit/README.md

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+# [mpy-lib](https://github.com/micropython-Chinese-Community/mpy-lib)
+
+## SHT3x 
+
+Humidity and Temperature Sensor micropython driver, **8bit** I2C address mode.
+
+![](sht30.jpg)
+
+
+## ESP32 example
+
+```python
+from machine import I2C, Pin
+from time import sleep_ms
+from sht3x import SHT3x
+
+i2c = I2C(0, sda=Pin(21), scl = Pin(22))
+
+sht30 = SHT3x(i2c)
+
+while True:
+    sht30.measure()
+    print(sht30.ht())
+    sleep_ms(1000)
+```
+
+## API
+
+- SHT3x.**measure()**  
+Starting measurement.
+
+- SHT3x.**humidity()**  
+get humidity.
+
+- SHT3x.**temperature()**  
+get temperature.
+
+- SHT3x.**ht()**  
+get humidity and temperature.
+
+- SHT3x.**config(mode = 0x240b, delay = 6, decimal = 1)**  
+  - mode, measurement command. Please see [mode table](#mode) below.
+  - delay, measurement duration time
+    - low repeatability, 4ms
+    - Medium repeatability, 6ms (default)
+    - High repeatability, 15ms 
+  - decimal, number of digits after decimal point
+
+- SHT3x.**heater(on=0)**  
+Turn on/off internal heater.
+  - on=1, turn internal heater
+  - on=0, turn off internal heater
+
+- SHT3x.**status()**  
+Read **Status Register**
+
+- SHT3x.**clear_status()**  
+Clear **Status Register**
+
+- SHT3x.**reset()**  
+Soft Reset
+
+### <a name='mode'>mode table</a>
+| mode | Repeatability | Measurement | mps |
+|-|-|-|:-:|
+| 0x2c06 | High | Single Shot| - |
+| 0x2c0D | Medium | Single Shot | -|
+| 0x2c10 |  Low | Single Shot | -|
+| 0x2400 | High | Single Shot|- |
+| 0x240b (default)| Medium | Single Shot |-|
+| 0x2416 |  Low | Single Shot | -|
+| 0x2032 | High | Periodic mode | 0.5|
+| 0x2024 | Medium | Periodic mode | 0.5|
+| 0x202F | Low | Periodic mode | 0.5|
+| 0x2130 | High | Periodic mode | 1|
+| 0x2126 | Medium | Periodic mode | 1|
+| 0x212d | Low | Periodic mode | 1|
+| 0x2236 | High | Periodic mode | 2|
+| 0x2220 | Medium | Periodic mode | 2|
+| 0x222b | Low | Periodic mode | 2|
+| 0x2334 | High | Periodic mode | 4|
+| 0x2322 | Medium | Periodic mode | 4|
+| 0x2329 | Low | Periodic mode | 4|
+| 0x2737 | High | Periodic mode | 10|
+| 0x2721 | Medium | Periodic mode | 10|
+| 0x272a | Low | Periodic mode | 10|  
+
+
+please note, In order to simplify the code, crc8 checksum is ignored.
+
+From [microbit/micropython Chinese community](https://www.micropython.org.cn).  

sensor/SHT3x/I2C_8bit/sht30.jpg

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+# mpy-lib
+# SHT3x humidity and temperature sensor 8bit I2C micropython drive
+# ver: 1.0
+# License: MIT
+# Author: shaoziyang
+# https://github.com/micropython-Chinese-Community/mpy-lib
+
+from time import sleep_ms
+
+class SHT3x():
+
+    def __init__(self, i2c, addr = 68):
+        self.i2c = i2c
+        self._addr = addr
+        self.ver = '1.0'
+        self.info = 'SHT3x I2C drive for micropython'
+        self._mode = 1
+        self._cmd = 0x240b
+        self._delay = 6
+        self._decimal = 1
+        self._tb = bytearray(2)
+        self._rb = bytearray(3)
+        self._ht = bytearray(6)
+        self._T = 0
+        self._H = 0
+        self.reset()
+
+    def status(self):
+        self.write(0xf32d)
+        self.i2c.readfrom_into(self._addr, self._rb)
+        return self._rb[0]*256 + self._rb[1]
+
+    def clear_status(self):
+        self.write(0x3041)
+
+    def write(self, cmd):
+        self._tb[0] = cmd>>8
+        self._tb[1] = cmd
+        self.i2c.writeto(self._addr, self._tb)
+
+    def reset(self):
+        self.write(0x30a2)
+    
+    def heater(self, on=0):
+        if on: self.write(0x306d)
+        else:  self.write(0x3066)
+    
+    def config(self, mode = 0x240b, delay = 6, decimal = 1):
+        t = mode >> 8
+        self._mode = 1 if t == 0x24 or t == 0x2C else 0
+        self._cmd = mode
+        self._delay = delay
+        self._decimal = decimal
+        self.write(mode)
+        
+    def measure(self):
+        if self._mode:
+            self.write(self._cmd)
+            sleep_ms(self._delay)
+        self.write(0xe000)
+        self.i2c.readfrom_into(self._addr, self._ht)
+        self._T = self._ht[0]*256+self._ht[1]
+        self._H = self._ht[3]*256+self._ht[4]
+
+    def humidity(self):
+        return round(100*self._H/65535, self._decimal)
+
+    def temperature(self):
+        return round(175*self._T/65535 - 45, self._decimal)
+
+    def ht(self):
+        return self.humidity(), self.temperature()