Update README to reflect new version of gfortran.

I'm assuming 4.7 still works, and the newest version on brew (4.8) also worked for me when I used it last night.
Merge pull request #2810 from danluu/gfortran_ver

Update README to reflect new version of gfortran
fix #2813
performance tweak to ObjectIdDict. fixes #2809
Update index.rst
Merge pull request #2823 from lbenitesanchez/patch-1

Update index.rst
document float32 literals, fixes #2821
update quaternion example code
document relative module paths
Update listing with new packages
Update packages documentation.
Add uninstallation instructions to README and other cosmetic updates.
Remove contrib/repackage_system_suitesparse3.make since we are now on SuiteSparse 4.
Some cleanups to README.
Remove link for the online REPL - now that the old webrepl is no
longer supported.
Few more README cleanups.
Point to the docs rather than to the manual in the README.
seekstart
Merge pull request #2833 from WestleyArgentum/seek

seekstart
fix #2829, regression in reload
fix #2832, const with multiple assignment
Merge branch 'master' of github.com:JuliaLang/julia
improve OpenBLAS 32/64bit mismatch error message
Merge pull request #2834 from jtriley/patch-1

improve OpenBLAS 32/64bit mismatch error message