Fix missing pyproject.toml build-backend

The PEP-518 mandated that all packages having the pyproject.toml
must specify the build-backend section [1]. This field was not
defined in Snippy pyproject.toml file previously. There has
been updates at least to setuptools [2] to allow compatibility
mode without this parameter.

The referred change [2] is very recent so it is not fully
understood why the installation has been (?) working when
this project has the pyproject.toml. The reason is likely
that the similar case is wide spread among Python projects
and it has been sorted out somehow.

This is not fully understood how this goes. Good reading in
[1] and [3] related to latest updates on Python packaging on
top of PEP-517 and PEP-518.

[1] https://www.bernat.tech/growing-pain/
[2] pypa/setuptools#1652
[3] https://www.bernat.tech/pep-517-518/

Signed-off-by: Heikki Laaksonen <[email protected]>

TODO.md

@@ -1,16 +1,11 @@
 ## WORKING
-   - [ ] Add description to cli and modify template settings to set it if provided.
-   - [ ] Add logic to name. This can be updated from REST. This should not do anything because of security?
-   - [ ] Add logic versions. Change version to content_versions in base? Same all content? Requires long lines for cli.py. How describe versions? Require key=value like version=1.1.1 format.
-   - [ ] Add logic source.
    - [ ] Fix creating/updating resource with invalid versions. The seal() cannot check if Cause not is_is because it generates incorrect error. For example GET ../<valid digest>/error shows error that digest not foind. See test_api_search_reference_field_012.
-   - [ ] Fix pinning of yaml that does not install globally. THe instructions are to use local but that could contain help to add the ~./local/bin to path.
+   - [ ] Fix pinning of yaml that does not install globally. The instructions are to use local but that could contain help to add the ~./local/bin to path.
    - [ ] Refactor Makefile to have python|python3|pypy|pypy3 as ${PYTHON}.
    - [ ] Test export/import Mkdn snippet with partial comments. The export must have the <not documented> tag and import must remove it.
    - [ ] How to compile psycopg2 for PyPY?
    - [ ] Add bash completion to Snippy. Check example from Poetry.
    - [ ] Fix cli -f file to see if this goes ot content filename attribute. Should not. -f|--file and content.filename are not the same.
-   - [ ] build-backend from pytest to Toml. This was mandatory from Pep 517 (?). People just not use it (or read) so it is defaulting. Better to have it explicitly.
    - [ ] Fix help text to use import --all instead of content specific commands. Or keep?
    - [ ] Why starting server calls collection initialization 4 times?
    - [ ] Starting the server again and import the default content again with --defaults causes server internal erro 500 because of UUID. The 500 should not be here because this is not internal error. Fix?
@@ -49,6 +44,7 @@
    - [ ] Fix (optimize) the order of SQL columns. Fixed length columns first. This should ? allow database to optimize the length of data. Is this the case?
 
 ## FEATURES
+   - [ ] Add decsription, name, versions and source to CLI? Or does this make the CLI too bloated? These can be updated via editor or REST API.
    - [ ] Add support to store any content in YAML files when server starts. Give path to folder that contains yaml files and import all?
    - [ ] Add combine on top of migrate and merge. The combine would allow adding for example a tag to an existing list of tags. This would be nice for CLI and could be used with RFC 6902 (JSON Patch) (if implemented).
    - [ ] Add support to search phrases like has 'active end'. This should return one result with default set but it returns two since each word is searched separately.

pyproject.toml

@@ -1,2 +1,6 @@
 [build-system]
-requires = ['setuptools>=38.6.0', 'wheel>0.31.0']
+requires = [
+    'setuptools>=38.6.0',
+    'wheel>0.31.0'
+]
+build-backend = "setuptools.build_meta"