chore: Documentation fixes and minor API update

[albertodev01]

Why?

There are some small error in the documentation and some missing methods to convert fraction classes to the new EgyptianFraction type.

What?

Added toEgyptianFraction methods and fixed some minor documentation mistakes.

Types of Changes

• New feature (non-breaking change which adds functionality) -->
• Documentation change

Checklist

• I have provided a description of the proposed changes.
• I added unit tests for all relevant code.
• I added golden tests for all UI changes.
• I added documentation for all relevant code.

[codecov]

Codecov Report

Merging #10 (9fd7ba1) into master (456e342) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #10   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          299       305    +6     
=========================================
+ Hits           299       305    +6     

Impacted Files	Coverage Δ
lib/src/extensions/fraction_string.dart	100.00% <ø> (ø)
lib/src/utils/exceptions.dart	100.00% <ø> (ø)
lib/src/core.dart	100.00% <100.00%> (ø)
lib/src/egyptian.dart	100.00% <100.00%> (ø)
lib/src/mixed.dart	100.00% <100.00%> (ø)

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