Find more liblsl variants

[tstenner]

This PR searches a bit harder for liblsl, namely liblsl with or without debug suffices (-debug), bitness suffices (32, 64 depending on the platform) and in the pylsl.py directory and the default system search path.

Also, users can set the PYLSL_LIB environment variable (see #13) to load a specific library.

[cboulay]

Just the small change to move the if 'PYLSL_LIB' block to the top of the function. Other than that it looks good.

[cboulay]

Have you fixed the CI builds since this PR?

[tstenner]

The CI builds just fine now, I've also switched from full builds to the prebuilt binaries fron sccn/liblsl releases so the build is a lot faster now (6m->21s). I'm not sure if the tag is correct (cp27-cp27m-manylinux2010_x86_64). I've already set the python-tag to py3, but I'm hoping that you know the magic setup.py parameter to fix it :-)

[cboulay]

I've never had to do anything to specify the tag because cibuildwheel takes care of that automatically. Specifying the tag manually won't make pypi accept it, it has to pass auditwheel.

[cboulay]

I think you can just do auditwheel repair <wheelname.whl> and it will create a properly named wheel for you.

[tstenner]

I removed the has_ext = True in the setup.py because even though not a pure python package it doesn't depend on a specific python version. bdist_wheel now generates the right packages automatically, so auditwheel doesn't have to do anything.

[tstenner]

I checked the resulting package; auditwheel is happy:

pylsl-1.13.2-py2.py3-none-any.whl is consistent with the following
platform tag: "manylinux2010_x86_64".

The wheel references external versioned symbols in these system-
provided shared libraries: librt.so.1 with versions {'GLIBC_2.2.5'},
libm.so.6 with versions {'GLIBC_2.2.5'}, libgcc_s.so.1 with versions
{'GCC_3.3', 'GCC_4.2.0', 'GCC_3.3.1', 'GCC_3.0'}, libpthread.so.0 with
versions {'GLIBC_2.3.2', 'GLIBC_2.3.3', 'GLIBC_2.2.5'}, libc.so.6 with
versions {'GLIBC_2.7', 'GLIBC_2.4', 'GLIBC_2.3.2', 'GLIBC_2.9',
'GLIBC_2.3', 'GLIBC_2.2.5', 'GLIBC_2.8'}

Also, both Python 2.7, 3.4 and 3.7 from the manylinux2010 image can install the wheel produced by the CI and run the examples so I think we could merge it.

[tstenner]

And I've added the manylinux1 builds.