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)
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
Merge pull request #6902 from tanmaykm/readcsv

better handling of empty file in readdlm.
tab substitution of LaTeX symbols in REPL (fixes #6340)
make deserialization backwards compatible (allow reading old data)

make serializing strings even faster
Merge branch 'master' of github.com:JuliaLang/julia
remove duplicate LaTeX symbols (font variations) ... fortunately, it looks like the most reasonable choice is listed first in the unicode.xml file
add \sqrt and \cbrt substitutions
fix #6909