feat: Introducing a new parser for all utils

This is a new fully working parser for the arg options.
The parser is written generically so it can be used in all diffutils tools.
The first implementation is done with sdiff. I already have a version for cmp as well.

I checked and discarded clap as tool, as the requirements are very individual and would require extensive tweaking of the clap functionality.

Features:

- Allows options to be abbreviated, e.g. --wi instead of --width
- Allows input like in GNU utils, e.g. the following are all identical
  - diff --ignore-case --minimal --width=50 file_a file_b
  - diff --ignore-case --minimal --width 50 file_a file_b
  - diff -i -d -w 50 file_a file_b
  - diff -id -w50 file_a file_b
  - diff -idw50 file_a file_b
- A number parser is available, which parses option arguments
  with optional byte units, e.g. =1024 or =1024KiB
- Default handling for --version and --help
- Returns the params or an Error Enum, which makes it library friendly.
- Contains error handling for the typical parsing errors:
  -- missing and extra operands
  -- invalid, ambiguous or conflicting options
  -- missing or not allowed option arguments
- Provides error text functions, e.g. add executable and 'Try --help' to message.

Author: Gunter Schmidt

Cargo.toml

@@ -46,7 +46,14 @@ harness = false
 
 [features]
 # default = ["feat_bench_not_diff"]
-# Turn bench for diffutils cmp off
+# instead of limiting to KiB, MiB, etc, one can write kib, mib, Mb or whatever case.
+feat_allow_case_insensitive_number_units = []
+# Disable bench for diffutils cmp
 feat_bench_not_cmp = []
-# Turn bench for diffutils diff off
+# Disable bench for diffutils diff
 feat_bench_not_diff = []
+# Enables a check on options defined in NOT_YET_IMPLEMENTED.
+# If on the parser will return an error message in these cases.
+# This is preferable when running the util as unsupported options
+# are pointed out to the user, but can make tests fail. 
+feat_check_not_yet_implemented = []