Adding Arb in CMakeList. Arb can be used -DWITH_ARB=yes
Modified Travis to install ARB if WITH_ARB is set

Also updated bin/test_travis.sh
Fix comment message
Update mpfr install command in .travis.yml

The updated command is: sudo apt-get install libmpfr-dev
Added explicit path for gmp
Travis: remove "-v" from tar calls
Remove the --with-gmp
Specify the location of libgmp.so
Installing Arb as an extension of flint

Also removed -v flags to supress output in untar
Arb: specify MPFR library location
Arb: give the GMP paths to "make install"

Thanks to Isuru Fernando (@isuruf) for spotting this.
Merge branch 'arb-fix' into arb

Conflicts:
	.travis.yml
Adding include flags for arb in CMAKE

This is perhaps not the best way, but works for me
@certik will review this once he is back from
vacation
Added `bernoulli` function

* Linked fmpq_t and  mpq_class
* Added tests.
Uodated bernoulli test to check exception if ARB is not present
Upgraded ARB from 2.1.0 to 2.2.0

This should fix issues in travis builds
Updated `bin/test_travis.sh` to link installed libraries for arb
Added `Zeta` class

* Added the basic API
* Added the function definitions
Added tests for zeta, updated test_travis.sh

test_travis.sh now also searches for /usr/local/lib for libarb.so
include flint
Merge branch '4' into arb

Conflicts:
	bin/test_travis.sh