Multiple ways to specify version string through environment variables:
- `ESPURNA_BUILD_FULL_VERSION` to set full version string
By default it is empty, and the version is combined using the values specified below
- `ESPURNA_BUILD_VERSION` to modify the first part of the version string (1.15.0-dev)
By default, uses espurna/config/version.h APP_VERSION value
- `ESPURNA_BUILD_REVISION` to specify revision part of the version string
For example 12345678, which is expanded as either .git12345678 or -git12345678
(depending on whether the version string contains hyphen)
By default, use git to retrieve the first 8 characters of the current HEAD SHA value
- `ESPURNA_BUILD_VERSION_SUFFIX` to specify build metadata part of the string
For example nightly20210607, which is added to the full version as 1.15.0-dev+nightly20210607
Empty by defauld

Adds -t build-and-copy which uses the values above to copy firmware.bin, configurable with:
- `ESPURNA_BUILD_NAME` to set the suffix of the filename.
By default, uses the $PIOENV (aka the string after the env: in the .ini file)
- `ESPURNA_BUILD_DESTINATION` to specify where to copy the .bin files
By default, uses $PROJECT_DIR

Resulting file is stored at:
${ESPURNA_BUILD_DESTINATION}/${ESPURNA_BUILD_FULL_VERSION}/espurna-${ESPURNA_BUILD_FULL_VERSION}-${ESPURNA_BUILD_NAME}.bin

In addition, modify generate_release_sh.py to use the new environment variables.