Refactor with_interval_precision -> setprecision etc.

[dpsanders]

Changes:

• set_interval_precision(x) -> setprecision(Interval, x).
• get_interval_precision() -> precision(Interval)
• set_interval_rounding(x) -> setrounding(Interval, x)
• get_interval_rounding() -> rounding(Interval)

in accordance with JuliaLang/julia#13232
i.e. don't invent a new function, just add methods to the (now) standard functions.

[coveralls]

Coverage decreased (-0.4%) to 93.923% when pulling 4346192 on refactor_precision_names into 6b531a7 on master.

[lbenet]

I'll consider the last two commits, since the rest is contained in #100.

[lbenet]

I don't quite understand why this is written like this.

Isn't it enough to add @compat when it is needed, avoiding this if?

[dpsanders]

I'm not sure if we could use @compat, but since these commands, in particular setprecision, occur a lot, I would not like to do so.

This is certainly ugly, but I'm not sure if there's a simple way to improve it.

[lbenet]

Probably a good idea to rebase before merging (once #100 is merged).

[coveralls]

Coverage decreased (-0.7%) to 93.923% when pulling 83301ca on refactor_precision_names into bafad67 on master.

[coveralls]

Coverage decreased (-0.4%) to 93.923% when pulling 3393e54 on refactor_precision_names into d1905e8 on master.

[coveralls]

Coverage decreased (-0.4%) to 93.923% when pulling 3393e54 on refactor_precision_names into d1905e8 on master.

[coveralls]

Coverage decreased (-0.4%) to 93.577% when pulling 1c804e3 on refactor_precision_names into c23970c on master.

[lbenet]

The problem with the tests (0.5) may be solved by rebasing...

[coveralls]

Coverage decreased (-0.1%) to 93.913% when pulling e073fa5 on refactor_precision_names into c23970c on master.