Make minor performance improvements

[dcslagel]

Description:

This pull-request is an attempt to improve performance:

• Reduce regex compiles by changing them to or with |
• Move the import of OpenPyx from init.py to las.py::to_excel(). This saves about .038 seconds on Lasio loading.
• Move the split_on_whitespace regex so that it is compiled only once and called directly when needed.

Performance Results:

--------------------------------------------------- benchmark: 1 tests ---------------------------------
Name (time in ms)               Min       Max      Mean  StdDev    Median     IQR  Outliers    OPS  Rounds  
--------------------------------------------------------------------------------------------------------
test_read_v12_sample_big     891.9103  901.8956  895.0018  4.0155  893.1709  4.0403       1;0  1.1173   5
--------------------------------------------------------------------------------------------------------

This is a small amount faster than previous performance, which was (roughly):

test_read_v12_sample_big     944.9445  957.4294  950.0452

Test Coverage:

Name                       Stmts   Miss  Cover
----------------------------------------------
lasio/__init__.py              8      0   100%
lasio/convert_version.py      20     20     0%
lasio/d1.py                   11     11     0%
lasio/defaults.py             11      0   100%
lasio/examples.py             42     10    76%
lasio/excel.py                88     34    61%
lasio/exceptions.py            6      0   100%
lasio/las.py                 443     62    86%
lasio/las_items.py           199     29    85%
lasio/las_version.py          50     14    72%
lasio/reader.py              432     27    94%
lasio/writer.py              171      9    95%
----------------------------------------------
TOTAL                       1481    216    85%

--
Let me know if this change could be accepted (or rejected) or
needs some additional changes to be approved and merged.

Thank you,
DC

[kinverarity1]

Looks great thank you!

[kinverarity1]

If you think this is ready to merge I'm happy to

[dcslagel]

Yes, this is ready go in.
Thanks!
DC