feature/underline-strikethrough

[lyind]

Description

This adds fontstyle.Type constants Underline and Strikethrough to make use of gofpdf's U (underline) and S (strike-through) font styles.

As those are often required to easily render underlined or stroke-through text, explicitly mentioning them in the constants should benefit many users of the library.

Related Issue

Checklist

check with "x", ONLY IF APPLIED to your change

• All methods associated with structs has func (<first letter of struct> *struct) method() {} name style.
• Wrote unit tests for new/changed features.
• Followed the unit test when,should naming pattern.
• All mocks created with m := mocks.NewConstructor(t).
• All mocks using m.EXPECT().MethodName() method to mock methods.
• Updated docs/doc.go and docs/*
• Updated example_test.go.
• Updated README.md
• New public methods/structs/interfaces has comments upside them explaining they responsibilities
• Executed make dod with none issues pointed out by golangci-lint

[lyind]

Using styles that contain U or S yields the expected result (underline, strike-through text rendered) in practice.

Could somebody please have a look, if this change makes sense conceptually?

I would then add the necessary tests/docs.

[Fernando-hub527]

Using styles that contain U or S yields the expected result (underline, strike-through text rendered) in practice.
Could somebody please have a look, if this change makes sense conceptually?
I would then add the necessary tests/docs.

I believe this is a great feature