Use official spelling for W-8BEN

It's W-8BEN (or sometimes W-8 BEN), not W8-BEN.

Drop closing colon from tags

The syntax in ledger is tag: -- the actual tag is tag, not tag:.
The guide was inconsistent about that.

TaxImplication: improve wording on what W2 means

W2 really means it's income reportable as USA federal income by an
employee on their W2.

TaxReporting: new documentation tag for tax info.

This new optional documentation tag goes along with TaxImplication tag
to explain how the TaxImplication ended up being true.

GrantLocation: new tag to help w/ 990 Schedule I&F

This new tag, for use in Expense accounts, will assist in collecting
data for filing Form 990 Schedule I (for USA domestic grants) and
Schedule F (for foreign grants).

E.g. of invoice for conference w/ split IncomeType

An example of an invoice for a conference where the income type is split
between RBI and Donations. Include a ledger reporting example that
shows the total of donations, and explain in the documentation why
that's useful.

Standardize on 'Expenses" in account names

We've concluded that the top-of-hierarchy account name for Expenses
should be Expenses, not Expense. This change normalizes the tutorial
text and examples to Expenses.

Initial documentation for Income accounts, including tagging requirements.

Implemented in the config-accounts.ledger is an incomeChecker() function that
matches the documentation requirements.

Initial documentation of the TaxImplication tag.
Includes declaration in the configuration for TaxImplication tag.

First documentation for the Entity: tag.

Included also is a ledger command to get the list of all tag values.

Fix awkward descriptions: details on the tags were under the account tag requirements.

Thus, I factored the text regarding the linking to documents that was in the
Expense account section into the section on describing the tags themselves,
and then merely linked back to that.

Initial documentation of the Program: tag.
Includes introduction of the section about making use of these tags.

Add example that explains very briefly how tagging works in Ledger CLI.

Since this system relies so heavily on tagging, even though we assume the
reader is generally familiar with Ledger CLI, it's worth ensuring they know
the basics of how tagging works.

Also added herein is the example used in the text over to the Ledger file
itself.

Initial documentation for Expense: documentation requirements.

This includes some additions to the example ledger files.