Make project PlatformIO compilable

[maxgerhardt]

PlatformIO is a Python commandline tool with supplementary VSCode and CLion extensions for building embedded firmwares in a platform-independent way. PlatformIO is also able to generate project files for 11 desktop IDEs in which the project can be seamlessly edited and uploaded.

Based on issue #206 and the related community topic I've created

• the needed platformio.ini configuration file so that
  • this is a PlatformIO-recongized project
  • all build and upload options that the Makefile would apply for compilation are applied during the PlatformIO build
• scripts that reproduce the Makefile's behavior regarding creating a version.c from git describe
• precompiled uploader tool lpc21isp for Windows (compiled with Visual Studio) and Linux

So, building this firmware on the CLI is as simple as having PlatformIO installed (pip install platformio) and executing pio run for compiling and pio run -t upload for upload. (Or use the VSCode plugin to nicely load and edit the project). The experience is that it's an easily loadable, editable and uploadable project.

The Makefile buildsystem still works exactly as before, and has been slightly adapted to be PlatformIO as well as Makefile compilable. These changes include renaming .s files to .S (PIO treats these extension differently) and removing the PlatformIO-generated version.c file.

[GitLang]

Builds fine directly from an unzip. Just the two trivial warnings which we've had all along -

src\cr_startup_lpc21.S:63:1: warning: "/*" within comment [-Wcomment] /*****/

src\cr_startup_lpc21.S:79:1: warning: "/*" within comment [-Wcomment] /*****/

Also, again trivial, PlatformIO complains if there isn't an /include directory, empty or not.