Avoid calling malloc to compute the SHA256 hash of file.
Now getsha() reads chunks of 1MiB maximum until EOF.

- Correct Markdown links
- Format sup files into a list
- Clarify example comments
- Add field information for binary*
- Fix typos
- Set everything that is not code to lowercase :)

@jaromil TODO: add sup.git to code.dyne.org

we adopt the standard shell error code (1) on exit.
messaging is slightly simplified.
static build now targets musl, getpwuid is not a problem.

included a FIPS-180-2 compliant SHA-256 implementation

Added use of getpwuid to resolve usernames found /etc/passwd
bumped version to 0.2 and improved -l, now also showing flags
error messages go to stderr, all others go to stdout.

* Check return value of lstat

  - Build with -O2 -Wall by default
* Clean up some warnings

  - chdir+chroot
* Added CHRDIR to chdir after chrooting
* Fix support to 'run any command'