Add FreeBSD CI badge to the README

Also do a bit of reformatting and simplification, and remove the 0.6
badge since the package no longer supports 0.6 and there are no badges
for newer versions.

Author: ararslan

README.md

@@ -2,21 +2,21 @@
 
 Special mathematical functions in Julia, including Bessel, Hankel, Airy, error, Dawson, sine and cosine integrals,
 eta, zeta, digamma, inverse digamma, trigamma, and polygamma functions.
-Most of these functions were formerly part of Base.
+Most of these functions were formerly part of Base in early versions of Julia.
 
-Note: On Julia 0.7, this package downloads and/or builds
-[openspecfun](https://github.com/JuliaLang/openspecfun), which is no longer built as part
-of Julia.
-Binaries are available for macOS, Windows, and Linux (glibc >= 2.6).
+This package downloads and builds [openspecfun](https://github.com/JuliaLang/openspecfun).
+Binaries are available for macOS, Windows, FreeBSD, and Linux (glibc >= 2.6).
 To force compilation of the library from source, set an environment variable called
 `JULIA_SPECIALFUNCTIONS_BUILD_SOURCE` equal to `true` before running `Pkg.build`.
 
-[![Travis](https://travis-ci.org/JuliaMath/SpecialFunctions.jl.svg?branch=master)](https://travis-ci.org/JuliaMath/SpecialFunctions.jl)
-[![AppVeyor](https://ci.appveyor.com/api/projects/status/ccfgkm2cjcggu158/branch/master?svg=true)](https://ci.appveyor.com/project/ararslan/specialfunctions-jl/branch/master)
-[![Coverage Status](https://coveralls.io/repos/github/JuliaMath/SpecialFunctions.jl/badge.svg?branch=master)](https://coveralls.io/github/JuliaMath/SpecialFunctions.jl?branch=master)
+| System | Test Status |
+| :----- | :---------: |
+| Linux/macOS | [![Travis](https://travis-ci.org/JuliaMath/SpecialFunctions.jl.svg?branch=master)](https://travis-ci.org/JuliaMath/SpecialFunctions.jl) |
+| Windows | [![AppVeyor](https://ci.appveyor.com/api/projects/status/ccfgkm2cjcggu158/branch/master?svg=true)](https://ci.appveyor.com/project/ararslan/specialfunctions-jl/branch/master) |
+| FreeBSD | [![Cirrus](https://api.cirrus-ci.com/github/JuliaMath/SpecialFunctions.jl.svg)](https://cirrus-ci.com/github/JuliaMath/SpecialFunctions.jl) |
 
-Latest release:
-[![SpecialFunctions](http://pkg.julialang.org/badges/SpecialFunctions_0.6.svg)](http://pkg.julialang.org/?pkg=SpecialFunctions)
+Coverage:
+[![Coveralls](https://coveralls.io/repos/github/JuliaMath/SpecialFunctions.jl/badge.svg?branch=master)](https://coveralls.io/github/JuliaMath/SpecialFunctions.jl?branch=master)
 
 Documentation:
 [![](https://img.shields.io/badge/docs-stable-blue.svg)](https://JuliaMath.github.io/SpecialFunctions.jl/stable)