Use platformio to build against multiple boards

[4-20ma]

ModbusMaster version

1.0.0

Arduino IDE version

any

Arduino Hardware

any

Platform Details

any

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Feature Request

Narrative:

As a project owner
I want my library to compile cleanly for multiple boards
So that it may be used on a wide variety of hardware

Acceptance Criteria:

Scenario 1: all boards
Given board is one of uno | due | huzzah | genuino101 | teensy31
When  `make` or `make all` is executed
Then  target compiles cleanly

Scenario 2: specific board
Given board is one of uno | due | huzzah | genuino101 | teensy31
When  `make <board>` is executed
Then  target compiles cleanly

Scenario 3: travis-ci
Given board is one of uno | due | huzzah | genuino101 | teensy31
When  `make build` is executed with PLATFORMIO_BOARD=<board>
Then  targets compile cleanly