Constructor and begin() API compatibility

This release is the culmination of working with contributors on comprehensive compatibility with the SoftwareSerial initialization on platforms from Arduino AVR to ESP8266 and ESP32 (POLS achieved).

6.1.1

Fix for local relative #include

New feature, a.k.a. "9bit": Supports parity bit on TX and RX and 2 stop bits

6.1.0

Bump minor version for first release of Parity feature.

6.0.0

Throw major release number to stop confusion over ctor/begin() split …

5.4.0

Version 5.4.0 with internal changes stablized on ESP8266 and ESP32.

Performance / error improvements for TX

5.3.5

Bit writing computation is now concurrent to output timing, improves …

5.3.4

Check m_rxValid in flush(). Fixes #118

5.3.3

ghostl array compatibility: aggregate initialization, no implicit cas…

Fix for Arduino SAMD (Zero, MKR1000, M0)

5.3.2

Fix ghostl for Arduino SAMD (Zero, MKR1000, M0)

README update

Offer more clear guidance for matching versions of EspSoftwareSerial to ESP8266 Arduino.