Fix a few titles on doc pages

docs/en/modules/dht.md

@@ -1,7 +1,9 @@
-# dht Module
+# DHT Module
 
 ## Constants
-`dht.OK` (0), `dht.ERROR_CHECKSUM` (1), `dht.ERROR_TIMEOUT` (2)
+Constants for various functions.
+
+`dht.OK`, `dht.ERROR_CHECKSUM`, `dht.ERROR_TIMEOUT` represent the potential values for the DHT read status
 
 ## dht.read()
 Read all kinds of DHT sensors, including DHT11, 21, 22, 33, 44 humidity temperature combo sensor.

docs/en/modules/i2c.md

@@ -1,4 +1,4 @@
-# i2c Module
+# I²C Module
 
 ## i2c.address()
 Setup I²C address and read/write mode for the next transfer.

docs/en/modules/pwm.md

@@ -1,4 +1,4 @@
-# pwm Module
+# PWM Module
 
 ## pwm.close()
 Quit PWM mode for the specified GPIO pin.

docs/en/modules/spi.md

@@ -1,4 +1,4 @@
-#spi module
+# SPI Module
 All transactions for sending and receiving are most-significant-bit first and least-significant last.
 For technical details of the underlying hardware refer to [metalphreak's ESP8266 HSPI articles](http://d.av.id.au/blog/tag/hspi/).