Speeding up running the tests

@mahrud is already working on this.

Since Dec 17, 2020.

Here is a test:
```m2
i1 : elapsedTime check_1 "Macaulay2Doc"
-* running test 1 of package Macaulay2Doc in file:
../../Macaulay2/packages/Macaulay2Doc/doc9.m2:230:1:
rerun with: check_1 "Macaulay2Doc" *-
-- 9.86182 seconds elapsed
```
And the content of the test that took almost 10 seconds? Here it is:
https://github.com/Macaulay2/M2/blob/afaa83b5c6062dcbfc7f383bf4786d17ed0a0c3d/M2/Macaulay2/packages/Macaulay2Doc/doc9.m2#L227-L229
This is _objectively_ bad.

Here is the reason: when `(check, ZZ, String)` is called, two things happen:
1. `needsPackage (pkg, LoadDocumentation => true)`
https://github.com/Macaulay2/M2/blob/afaa83b5c6062dcbfc7f383bf4786d17ed0a0c3d/M2/Macaulay2/m2/testing.m2#L46
2. `loadPackage(pkg#"pkgname", LoadDocumentation => true, Reload => true)`
https://github.com/Macaulay2/M2/blob/afaa83b5c6062dcbfc7f383bf4786d17ed0a0c3d/M2/Macaulay2/m2/testing.m2#L31

Loading the documentation is necessary only because some authors have added package tests after `beginDocumentation()`. I see the appeal of this, especially since you can clearly put the tests near their respective documentation:
```m2
document{ key => "2 + 2",
EXAMPLE "2 + 2",
TEST "assert(2 + 2 = 4)"}
```
However, at least for `Macaulay2Doc`, this is slowing down running the tests **very** significantly, as the example above demonstrates.

Here are the two solutions I see:
1. use `capture` for tests instead (see #1689)
2. remove `LoadDocumentation => true` in `check` and enforce that all `TEST`s must appear before `beginDocumentation`
3. do one of the suggestions above, but only for Macaulay2Doc

@mikestillman @DanGrayson any thoughts on either of these?

This is somewhat a companion to #1480, as it speeds up testing of Macaulay2Doc very very significantly!

Related: #992.