my @lines = split /\n/, $m;

my %m;
my $curr_index;
foreach my $line (@lines)
{
    $line =~ /^\s*(\w+)?\s*:\s*(.*)$/;
    next unless $1 || $2;

    unless (defined $curr_index)
    {
        die "First line doesn't have a key\n" unless $1;
        $m{$1} = $2;
        $curr_index = $1;
        next;
    }

    if ($1)
    {
        $m{$1} = $2;
        $curr_index = $1;
        next;
    }

    $m{$curr_index} .= "\n$2";
}