Release v1.0.0

Changes to support julia v0.7, removal of compat statements

Release v0.5.0

Removes Dates from REQUIRE, updates travis build config, drops older versions of julia

SGP4 v0.4.0

Allow propagation by specifying dtmin, change the way multiple satellites are handled, and add v0.6 to the Travis config.

Fix depwarns for julia-v0.6

Removes deprecation warnings for @test_approx_eq

Release v0.3.0

Primarily adds new SGP4Sat type.