Base documentation - minor revisions

Many revisions on the base.rst. Formated and added new examples, inserted some returned types, etc.
Corrections on base.rst previous commit

Removed type annotation of some functions
Corrected identation and comments
Make prompts and i-searches the same word length

`(reverse-i-search)` and `(i-search)` are different length prompts and so when switching search directions, the entire line shifts position.  I find it disorienting.  Fortunately, `reverse` and `forward` both have seven characters.  This very very minimal patch renames (i-search) to (forward-i-search).  It isn't how readline behaves, but I think it is better.

Similarly, `"help> "` becomes `" help> "` to keep the prompt start at the same location.
Add region-based findmin and findmax (closes #6716)
This adds an expm1 function for complex values. It uses the property that

cos(x) - 1 = -2*sin(x/2)^2

There is some cancellation error when real(z) ~ imag(z)^2/2 for small z, but otherwise is fairly stable.
add more tests
Merge pull request #6539 from simonbyrne/expm1

Adds an expm1 function for complex values.
formatting fixes
fix #6900, hashing dicts
more efficient hash for sets
better handling of empty file in readdlm.
fixes #6898
Merge pull request #6893 from mbauman/stable-repl-prompt

Make prompts and i-searches the same word length
add complex log1p (fix #3141)
doc: typo in output
Merge pull request #6894 from JuliaLang/teh/findminmax

Add region-based findmin and findmax (closes #6716)
faster and more compact serialization of symbols and strings
Set function performance: build up sets instead of copying and deleting
Merge pull request #6904 from stevengj/log1p

add complex log1p
Merge pull request #6905 from simonbyrne/patch-1

doc: typo in output