Allow non-delimiting quotes in space-delimited data

[janbridley]

Description

When testing a fixed-precision unit cell builder implementation, I ran into a pattern in AFLOW's tabular data that broke parsnip's parsing engine. To fix this, I added an extra conditional check to the space_delimited_data regular expression.
The new pattern allows for single-quoted strings that contain single quotes that are not followed by a space (as this would indicate a delimiting whitespace). I did need to use some non-capturing groups for this pattern, but there are no lookahead/lookbehinds or labeled groups so the expression should never get catastrophic.

- r"\'[^'])*\'"
+ r"\'(?:'[^\s]|[^'])*\'"
# Data delimited by single quotes, which may contain other single quotes as long as they are not followed by a space

See point 15 from the CIF spec for examples of the pattern that was encountered here.

Previously-invalid string examples:

'Michael O'Keeffe'
'C. H\'{e}rold'
'J. F. Mar\^{e}ch\'{e}'

Outstanding issues:

Data entries that end with two single quotes in a row and are the last entry in a loop row will be terminated by only one of the two single quotes. I could fix this with some lookahead checks, but at the cost of a significant performance hit.

Types of Changes

• Documentation update
• Bug fix
• New feature
• Breaking change¹

¹The change breaks (or has the potential to break) existing functionality and should be merged into the breaking branch

Checklist:

• I am familiar with the Development Guidelines
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• I have updated the changelog and added my name to the credits.