Add Mercury 1.0 to boards

[raliotech]

Mercury is a new Board introduced by Ralio Technologies.

• Based on ESP8266
• Support onboard 2x brushed dc motor driver (1A per channel)
• Support onboard 4x direct servo (3 pin connections
• Support onboard 1x direct Ultrasonic sensor (4 pin) connection
• Support onboard 2x direct Infra Red sensor (3 pin) connection
• VCC pin support up to 12V
• Onboard 5V and 3v3 pins
  

[raliotech]

@earlephilhower
Hello Sir, it would be great if you can help me fix this bug. the issue is arising in that part of the code that I haven't touched. Please help me fix this.

[mcspr]

(I am pressing the CI button btw)
Documentation syntax is broken, as it turns out :/ Lemme fix the escape and footnotes...

[raliotech]

Closing this PR and started a new one.
Fixing issues here: #9166