deprecate `readstring` to `read(io, String)`

[JeffBezanson]

This is more consistent with other read methods, and more easily extensible to other types of strings.

[jpfairbanks]

This sounds straightforward you just:

• remove the definition of readstring
• add the new method for read(s::IO, ::Type{String})
• @deprecate in the base/deprecated.jl
• chase down all the deprecation warnings in Base
• Update the docs
• Add NEWS entry

Are there any other steps?

[JeffBezanson]

Correct!

[jpfairbanks]

This example in the docs doesn't work .

"""
    open(f::Function, args...)

Apply the function `f` to the result of `open(args...)` and close the resulting file
descriptor upon completion.

**Example**: `open(readstring, "file.txt")`
"""

You could make an anonymous function. open(f->read(f, String), "file.txt") but that looks weird.

[jpfairbanks]

Also what do you do with this line in precompile.jl

precompile(Tuple{typeof(Base.open), typeof(Base.readstring), String})
?

[JeffBezanson]

I think open(f->read(f, String), "file.txt") is fine, or maybe open(read, "file.bin") instead.

The precompile line can just be deleted; those need to be regenerated periodically anyway.

[jpfairbanks]

Ok, I went with f-read(f,String) and deleted it. The PR is open and CI failed due to some documentation building stuff. I don't know what to do about the CI.