* apcssh: add descriptive error when required file(s) not passed
* create: dont create key+cert file when key isn't supported by NMC2
* config: fix usage messages re: key types
* p15 files: dont generate key+cert when it isn't needed (aka NMC2 doesn't support key)
* pkcs15: pre-calculate envelope when making the p15 struct
* pkcs15: omit key ID 8 & 9 from EC keys
* pkcs15: update key decode logic
* pkcs15: add key type value for easy determination of compatibility
* pkcs15: add ec key support
* pkcs15: separate functions for key and key+cert p15 files
* update README
see: https://github.com/gregtwallace/apc-p15-tool/issues/6
The code should auto-select the native ssl method if the ssl command is available on the UPS.
If this fails, install will drop back to the original install method used by this tool (which works on NMC2).
This was done for clearer separation of function. A subsequent update will (hopefully) make the SSL command more robust so it works for both NMC2 and NMC3.
The method for sending shell commands was also updated to use an interactive shell instead. This allows capturing responses of the commands which will be needed to deduce if devices are NMC2 or NMC3.
