Fix circular dependency in setup.py

[ucabvas]

Installing this package in a new virtualenv fails because setup.py tries to import pyod which in turn tries to import all its dependencies (numpy is in the error message in particular). However, it's setup.py's responsibility to install numpy and it gets imported before it's installed.

Fixing this by decoupling the version string from the pyod init file. For reference, this is the error we were seeing prior to the fix:

(env_pyod) ☁  ~VIRTUAL_ENV  pip install pyod
Collecting pyod
  Downloading https://files.pythonhosted.org/packages/08/bf/05bef83df97f81a6492818e0a42034e1bcc222894fd66bd4ce66c23a8654/pyod-0.5.4.tar.gz (44kB)
    100% |████████████████████████████████| 51kB 2.3MB/s
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/private/var/folders/v3/d3h954156117rd5xdlfh8c0d081dvn/T/pip-install-G3JNoB/pyod/setup.py", line 2, in <module>
        from pyod import __version__
      File "pyod/__init__.py", line 4, in <module>
        from . import models
      File "pyod/models/__init__.py", line 2, in <module>
        from .abod import ABOD
      File "pyod/models/abod.py", line 12, in <module>
        import numpy as np
    ImportError: No module named numpy

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/v3/d3h954156117rd5xdlfh8c0d081dvn/T/pip-install-G3JNoB/pyod/

[coveralls]

Pull Request Test Coverage Report for Build 156

• 1 of 2 (50.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.04%) to 96.076%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pyod/version.py	0	1	0.0%

Totals
Change from base Build 154:	-0.04%
Covered Lines:	2326
Relevant Lines:	2421

---

💛 - Coveralls

[yzhao062]

@ucabvas Thanks for submitting a fix. I am just back from vacation and would take a look tomorrow.

Just wonder whether the fix is fine with all platforms (win/mac/unix)? especially with './pyod/version.py'. What about using os.path.join(os.path.sep, 'pyod', 'version.py') instead?

[yzhao062]

@ucabvas Fantastic! The PR is merged and a new version is pushed to pypi(v0.5.6) :)
Removed one unnecessary delimiter to please the doc builder.

Thanks a lot for spotting this bug!