rename FirmwareUploader to arduino-fwuploader

[umbynos]

For consistency with other arduino tools we decided to rename the FirmwareUploader to arduino-fwuploader
The changes are similar to #21

[umbynos]

The CI is failing on windows because of go build -o {{.PROJECT_NAME}}. The-o flag forces the binary name, but on win it does not take care of adding automagically the .exe extension required on the OS. So I'm reverting that change. The default name for the go build command apparently is the name of the parent folder (and in this case the repo name). The repository name will be changed shortly

[umbynos]

I would like to follow this strategy:

1. approval
2. rename the repo to arduino-fwuploader
3. merge

[umbynos]

PS I did not rename the loader sketches inside firmwares/<module_name>/FirmwareUploader.<board>.ino.[bin/elf] because of:

1. this
2. They are the compiled version of this. And in my opinion is better to keep things consistent