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...

Seems to work with stdin

Deleted old argument struct tm* from search function (now using infos
stored in ttail_t.session )

add a -h --help option, deleted -l --logfile options
+ spliting the ttail_search_closest() & ttail_search_print_res() functions

Now we have a running minimal ttail :
src/ttail -d "Mar 6 00:29" -f '%B%n%d %H:%M' -l tests/samples/1.log -l tests/samples/1.1.log

Enhancement in comparison behavior + print function