Update description, legal (#3)

- Update legal info
- Update language description
  - Copy editing and line wrapping
  - Remove some references to NWB except as examples
  - I personally prefer not to use the cryptic pseudo word "data_type" or "neurodata_type" (with the underscore) and instead to use just "data type". I changed those throughout.
  - Add statement that under `namespace` > `schema`, `source` or `namespace` must be specified, but not both.
  - Fix comment saying that attributes can be specified for links
  - Remove "Schema specifications are stored in dict ``spec`` and relationship that make up the format.
consist of a list of Group specifications." which is not used as far as I can tell

Legal.txt

@@ -1,4 +1,4 @@
-“hdmf” Copyright (c) 2020, The Regents of the University of California, through Lawrence Berkeley National Laboratory (subject to receipt of any required approvals from the U.S. Dept. of Energy).  All rights reserved.
+“hdmf-schema-language” Copyright (c) 2020, The Regents of the University of California, through Lawrence Berkeley National Laboratory (subject to receipt of any required approvals from the U.S. Dept. of Energy).  All rights reserved.
 
 If you have questions about your rights to use or distribute this software, please contact Berkeley Lab's Innovation & Partnerships Office at [email protected].
 

license.txt

@@ -1,4 +1,4 @@
-“hdmf” Copyright (c) 2020, The Regents of the University of California, through Lawrence Berkeley National Laboratory (subject to receipt of any required approvals from the U.S. Dept. of Energy).  All rights reserved.
+“hdmf-schema-language” Copyright (c) 2020, The Regents of the University of California, through Lawrence Berkeley National Laboratory (subject to receipt of any required approvals from the U.S. Dept. of Energy).  All rights reserved.
 
 Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: