Allow updating existing releases

[ansasaki]

While in development phase, the user should be able to update an existing release.

In the best case, smap should be able to know which releases were released and which were not. Maybe it could be done with an special comment syntax for released releases. As in:

#@ released
LIBX_1_2_3
{
    global:
        symbol;
    local:
        *;
} ;

or simpler:

LIBX_1_2_3 # released
{
    global:
        symbol;
    local:
        *;
} ;