Dirdiff mmap - improve dirdiff performance using mmap

Changes:

• Use mmap for files with size greater than CHUNK_SIZE (curent set to 4096b);
• When "ignore blank line" retain content for rematch after remove blank lines;
• Remove blank lines now ignores lines with only spaces;
• All_same accept iter and runs faster;
• Convert large data to generators and small data to list;
• Use regex to normalize line ending;
• Apply regex.sub instead of apply_text_filters;
• Add tests for _files_same, all_same and remove_blank_lines.

Test executed:

• empty files (fastest equal, wont read files)
• 1b vs 1b file (fast equal, read both until end)
• 4mb vs 4mb file (slow equal, read both until end)
• empty vs 1b file (fast different, first chunk diff)
• 1b vs 4mb file (fast different, first chunk diff)
• 4mb vs 4mb file (slow different, read both until end)

cProfile Results:

• master branch: 34291 function calls in 0.337 seconds
• this branch: 1115 function calls in 0.069 seconds