Update debugSend / debugSend_P

[mcspr]

• remove varargs handling from debugSend and debugSend_P
• chain debugSend_P into basic _debugSend instead of duplicating code, pass va_list between them
• when possible, use stack buffer and fallback to heap buffer only when it is more that 64 chars
• check if new[] was successful

[mcspr]

Having remembered dev...mcspr:ws/optimize, what I did not is template size overhead. I'll inspect it more closely, but this does not look good :/

env:travis01

Size	Description
579280	templates, both inline
567008	templates, debugSend_P inline
558752	templates, debugSend inline
558288	templates, no inline
551840	old varargs
570832	debugSend varargs, debugSend_P as macro (basically, inline)
551920	debugSend varargs, debugSend
551856	debugSend_P, debugSend, _debugSend(format, va_list)
551952	debugSend_P, debugSend, inline _debugSend(format, va_list)

"inline" means inline __attribute__((always_inline))

Reverting the template part, but keeping other things