Fix buffer overflow

Increase the buffer size for strings by one byte to accomodate the
trail NULL expected by ei_decode_string:

    The string is copied to p, and enough space must be allocated. The
    returned string is null terminated so you need to add an extra byte
    to the memory requirement.
Prevent stack overflow

Large strings can overflow the stack:

    crash() ->
        cecho:start(0,0),
        S = lists:duplicate(8192*1024*2, "x"),
        cecho:mvaddstr(0,0,S).

Fix the problem by putting the data on the heap.
Added git versioning (new cecho.app.src)
Merge branch 'overflow' of https://github.com/msantos/cecho
Updated to rebar 2.5.1