[c/en] Fixed mistakes & added clarifications regarding the C standard

[MykBamberg]

• Reference to C23 constexpr constants

• Note on long long only being supported since C99

• Clarification about the _Bool/bool type in section on comparisons

• Fixed incorrect explanation about null statements

• Replaced boolean typedef, which in it's original form would not compile when using the C23 standard (which is due to become the default for gcc)

• Updated outdated information on binary literals

• Added %b binary conversion specifier

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