Fix typoes
Cosmetics

Change 'dump' to 'extract' strings,
remove second input from command line and make --extract a string parameter
Do not use .part suffix, cosmetics

Do not use .part suffix but create partfiles inside temporary volume.
Do not use SXI_SHA1_BIN_LEN.
Add cleanup code after file is renamed or unlinked.
Remove partfile is 0 hashes were restored.
Change help page and usage.
Print full help when bad args and --extract given