Fix some of the documentation std::io::fs

[nham]

Some of the fixes include:

• fixing mismatch between the documentation and the function parameters. (i.e. documentation references path parameter, but it's actually called from, or vice versa)

• A few Error sections were missing an "if" on the middle clause. For example, they used to be: "This function will return an error if [Thing], [Another Thing], or if [Yet Another Thing]." I added an "if" so it becomes "This function will return an error if [Thing], if [Another Thing], or if [Yet Another Thing]"

• The error sections previously started off with 3 different phrases:

  • "This function will return an error if ..."
  • "Will return an error if ..."
  • "This call will return an error if ..."

  I've standardized on the first phrase.