v0.1.3: Release BLAKE2S patch version 0.1.3

Changes in this release:
- Switch from GNU Make to AST NMAKE, vastly simplifying project
Makefiles with the latter's native Ada support.
- Support for building the b2ssum utility using GPRBuild.

* .github/workflows/blake2s.yml: Run CI with AST NMAKE.
* README.md:
- Switch from inline to reference style URLS.
- Reformat for 80 columns.
- Document that AST NMAKE is required now for building.
* alire.toml: Removed as ALIRE packages are created manually now.
* b2ssum.gpr: New GPRBuild project file for the b2ssum file hash
utility.
* bin/b2ssum.adb:
- Switch from renaming operators to 'use type', as b2ssum is written
in the 1995 version of Ada and the former causes GNAT to emit warnings
about hiding standard definitions.
- Quash false positive emitted by newer versions of AdaControl (as
shipped by Debian/Ubuntu).
* blake2s.gpr:
- Increment version to 0.1.3.
- Place object files in gnat/obj and libraries in gnat/lib. The sobj
and slib directories were a holdover from the prior GNU Make setup;
NMAKE allows for building static and dynamic libraries in the same
directory.
- Per the new Alire default, disable runtime checks and contracts.
* blake2s.nmk: New Nmakefile containing project defaults.
* blake2sn.aru
* blake2so.aru:
- Add MIT-0 copyright header.
- Add clarifying comments.
- Give unnecessary_use_clause a name (Use_Rule).
* gnat/makefile.nmk: New Nmakefile for building the BLAKE2s library
and executables using GNAT.
* makefile.nmk: New Nmakefile for toolchain-agnostic operations.