Refactor to improve the user experience with non-ASCII characters

[seisman]

See #2204 (comment) for background and the issue.

This PR solves the issue by:

• Generating the mapping dictionary based on the mapping tables in https://github.com/seisman/GMT-octal-codes
• Add the encoding tables to the documentation

Preview:
The tables of supported encodings are at
https://pygmt-dev--3206.org.readthedocs.build/en/3206/techref/encodings.html.

This page is in the "Technical Reference" section, as discussed in #2834.

Note to maintainers

Below is the script used to generate the Markdown tables in the documentation

from pygmt.encodings import charset

undefined = "\ufffd"
markdown = ""
for charset_name, mappings in charset.items():
    markdown += f"## Adobe {charset_name} Encoding\n\n"
    markdown += "| octal | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |\n"
    markdown += "|---|---|---|---|---|---|---|---|---|\n"
    for i in range(0o00, 0o400, 8):
        chars = [mappings.get(j, undefined) for j in range(i, i + 8)]
        if chars == [undefined] * 8:
            continue
        chars = [f"&#x{ord(char):04x};" for char in chars]
        row = f"\\{i:03o}"[:-1] + "x"
        markdown += f"| **{row}** | {' | '.join(chars)} |\n"
    markdown += "\n"

print(markdown)

[seisman]

In [19]: "Ω" == "Ω"
Out[19]: False

In [20]: "Δ" == "∆"
Out[20]: False

In [21]: import unicodedata

In [22]: unicodedata.name("Ω")
Out[22]: 'OHM SIGN'

In [23]: unicodedata.name("Ω")
Out[23]: 'GREEK CAPITAL LETTER OMEGA'

In [24]: unicodedata.name("Δ")
Out[24]: 'GREEK CAPITAL LETTER DELTA'

In [25]: unicodedata.name("∆")
Out[25]: 'INCREMENT'

We were using incorrect characters previously!

[seisman]

"Δ" != "∆".

[seisman]

In previous version, we maintained a big dictionary like:

 ✁✂✃✄☎✆✇✈✉☛☞✌✍✎✏

but here I decide to use:

\u0020\u2701\u2702\u2703\u2704\u260e\u2706\u2707

The main reasons are:

• Avoid having too many non-ASCII characters in the source code
• Some non-ASCII characters can't be displayed correctly in text editors or GitHub web UI

For similar reasons, in the documentation, I use HTML syntax like

  | ✁ | ✂ | ✃ | ✄ | ☎ | ✆ | ✇ |

[seisman]

As discussed in #2834, the documentation group is called "Technical Reference". Here the directory name is techref. Please let me know if you're OK with the name.

[weiji14]

Yep, ok with the title name. We could maybe add a short paragraph under this title to mention what this page is about? Also would be good to link to https://docs.generic-mapping-tools.org/6.5/reference.html.

[seisman]

Added in f2b3dcb.

[seisman]

Ping @GenericMappingTools/pygmt-maintainers for reviews and will self-approve and merge in one week if no further comments.

[weiji14]

Just some minor typos and one suggestion on adding a short descriptive paragraph in the Technical Reference page. Haven't checked every single character in the tables, but I trust that they're ok 🙂

[weiji14]

Yep, ok with the title name. We could maybe add a short paragraph under this title to mention what this page is about? Also would be good to link to https://docs.generic-mapping-tools.org/6.5/reference.html.