Adds the option -P --permissive.

Starts implementation for logfiles.

Now -P flag make ttail handle invalid files. When invalid file given the
minmax function set the file pointer and the minmax array to NULL.

May introduce bugs if the binary search function does not handles "holes"
in fp array or in minmax array...

Not done for stdin

ttail_set_flag_re_ex() and ttail_set_flag_re_ci()

For extended & case insensitive regex

Now we can specify a constant length to cut