Lots of features and cleanup of command line interface.

[ctb]

This contains many useful features that were implemented in #45 but aren't specific to the SBT stuff.

Specifically,

• add --with-cardinality;
• sniff gzip/bz2 format signature files;
• add -n/--num-results to search;
• more/better printout information;
• add --name, --name-from-first, and --singleton to sourmash compute
• make load_signatures into a generator;
• bump version to 1.1;

• Is it mergeable?
• make test Did it pass the tests?
• make coverage Is the new code covered?
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Was a spellchecker run on the source code and documentation after
  changes were made?

[codecov-io]

Current coverage is 83.10% (diff: 84.76%)

Merging #56 into master will increase coverage by 0.28%

@@             master        #56   diff @@
==========================================
  Files             8          8          
  Lines           908       1018   +110   
  Methods          37         37          
  Messages          0          0          
  Branches         44         44          
==========================================
+ Hits            752        846    +94   
- Misses          139        155    +16   
  Partials         17         17          

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[ctb]

The uncovered stuff is mostly error handling, so I'm going to get to it later...