Signature of digest_chunks restored to original, SHA1 used for Java digest name instead of SHA-1
Merge pull request #5 from KonstantinShemyak/select_digest_algorithms

Digest algorithms can be specified for "manifest -c".
Merge pull request #6 from KonstantinShemyak/improving_manifest_ui

Better usage messages when number of command-line arguments is wrong
Dummy .SF and .RSA are created
Getting SF file is moved to be a Manifest method
Added main manifest section, for SHA-1 so far
Drafted create_sf_file(), not tested
Bugfixes
Entries in the manifest are outputted in the order in which they were parsed
Signature file created.
RSA file created via calling an external executable with hardcoded key
Fix: algorithms were written in the SF file in python (not Java) style
Newline separator made an attribute of Manifest class.

To calculate digests over the manifest, it is not enough to store
key-value pairs. We also need the newline character, which was used
in the original manifest.

When the manifest is created, separator is set to the OS default.
When the manifest is loaded, separator is obtained from the input
by more or less ugly methods.