`Sexpr` macros in Rd files

[Mark-Eis]

Make "dynamic pages" reflecting values of tax_opts() e.g., here: –

Fiscal/man/pers_allow.Rd

Lines 17 to 23 in e087f57

	The standard Personal Allowance is the amount of taxable income on which there is no tax liability,
	currently £12,570.
	The personal allowance goes down by £1 for every £2 that
	\href{https://www.gov.uk/guidance/adjusted-net-income}{adjusted net income} is above an upper
	threshold, currently £100,000. This means the personal allowance is zero if taxable income is
	£125,140 or above.

[Mark-Eis]

And here: –

Fiscal/man/incometax.Rd

Lines 39 to 55 in 35f3518

	The standard Personal Allowance is the amount of taxable income on which there is no tax liability,
	currently £12,570. The personal allowance goes down by £1 for every £2 that
	\href{https://www.gov.uk/guidance/adjusted-net-income}{adjusted net income} is above an upper
	threshold, currently £100,000. This means the personal allowance is zero if taxable income is
	£125,140 or above.
	Hence currently in 2026: --
	\itemize{
	\item taxable income exceeding the standard personal allowance (in the simplest case £12,570) by
	an amount up to £37,700 attracts 20\% basic rate income tax;
	\item taxable income up to £100,000 overall and exceeding the standard personal allowance by
	amounts between £37,701 and £87,430 attracts 40\% higher rate income tax;
	\item taxable income above £100,000 overall exceeding the reduced personal allowance by amounts
	between £87,430 and £125,140 attracts 40\% higher rate income tax; and
	\item taxable income above £125,140 has no personal allowance and attracts 45\% additional rate
	income tax.
	}

[Mark-Eis]

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