* Always build spiffsimg (and make it build)
* Make sure that we have the offset before allowing the user to put it
into the output filename
* Fix the documentation and align the makefile with the docs
* Clean up the docs a bit more
* Revert to include building the 8mb size (for ESP8285)
* Added a spiffsimg target that does what you would expect
* Added support for HOSTCC (defaults to gcc)