Add support for Lesotho TIN

https://www.pwc.co.za/en/assets/pdf/vat-in-africa-2017.pdf

The format of the VAT registration number is TN0000000-0. It is called a tax identification number (TIN).
https://www.lra.org.ls/faqs
The difference between VAT number and TIN (Taxpayer Identification Number) is that:
- TIN is allocated to every Client who has registered with RSL for tax purposes. It is a unique number given to each registered Client and holds all the information regarding all the tax types that a taxpayer is registered for (including VAT).
- VAT number however is only allocated to a taxpayer who is registered for VAT.
https://www.lra.org.ls/registrationde-registration

Only one TIN is allocated for purposes of Income Tax, Customs and Excise, and VAT.
It looks like TIN No is a common naming.

Examples (I could only find these):

arthurdejong / python-stdnum