Use Versioneer (#70)

* Add versioneer

* Remove unnecessary try/catch in __init__.py

 - Version is no longer obtained by importing from __init__.py

.gitattributes

@@ -0,0 +1,2 @@
+# Added by versioneer
+euphonic/_version.py export-subst

MANIFEST.in

@@ -1 +1,3 @@
 include c/*.h
+include versioneer.py
+include euphonic/_version.py

euphonic/__init__.py

@@ -1,29 +1,25 @@
-__version__ = '0.2.2'
+from ._version import get_versions
+__version__ = get_versions()['version']
+del get_versions
 
-try:
-    # Create ureg here so it is only created once. However, this
-    # __init__.py needs to be imported by setup.py to find __version__,
-    # so allow pint import to fail as in this case pint might not be
-    # installed yet
-    from pint import UnitRegistry
-    ureg = UnitRegistry()
-    ureg.enable_contexts('spectroscopy')
-    ureg.define('@alias bohr = INTERNAL_LENGTH_UNIT')
-    ureg.define('@alias electron_mass = INTERNAL_MASS_UNIT')
-    ureg.define('@alias hartree = INTERNAL_ENERGY_UNIT')
-    ureg.define('@alias elementary_charge = INTERNAL_CHARGE_UNIT')
-    ureg.define('@alias K = INTERNAL_TEMPERATURE_UNIT')
+# Create ureg here so it is only created once
+from pint import UnitRegistry
+ureg = UnitRegistry()
+ureg.enable_contexts('spectroscopy')
+ureg.define('@alias bohr = INTERNAL_LENGTH_UNIT')
+ureg.define('@alias electron_mass = INTERNAL_MASS_UNIT')
+ureg.define('@alias hartree = INTERNAL_ENERGY_UNIT')
+ureg.define('@alias elementary_charge = INTERNAL_CHARGE_UNIT')
+ureg.define('@alias K = INTERNAL_TEMPERATURE_UNIT')
 
-    ureg.define('@alias angstrom = DEFAULT_LENGTH_UNIT')
-    ureg.define('@alias amu = DEFAULT_MASS_UNIT')
-    ureg.define('@alias eV = DEFAULT_ENERGY_UNIT')
-    ureg.define('@alias K = DEFAULT_TEMPERATURE_UNIT')
+ureg.define('@alias angstrom = DEFAULT_LENGTH_UNIT')
+ureg.define('@alias amu = DEFAULT_MASS_UNIT')
+ureg.define('@alias eV = DEFAULT_ENERGY_UNIT')
+ureg.define('@alias K = DEFAULT_TEMPERATURE_UNIT')
 
-    from .spectra import Spectrum1D, Spectrum2D
-    from .crystal import Crystal
-    from .debye_waller import DebyeWaller
-    from .structure_factor import StructureFactor
-    from .qpoint_phonon_modes import QpointPhononModes
-    from .force_constants import ForceConstants
-except ImportError:
-    pass
+from .spectra import Spectrum1D, Spectrum2D
+from .crystal import Crystal
+from .debye_waller import DebyeWaller
+from .structure_factor import StructureFactor
+from .qpoint_phonon_modes import QpointPhononModes
+from .force_constants import ForceConstants