Add build tag sqlite_math_functions

[nkt-dk]

Add build tag sqlite_math_functions to enable built-in scalar math functions using compiler flag SQLITE_ENABLE_MATH_FUNCTIONS. For reference: https://www.sqlite.org/lang_mathfunc.html.

I also updated the readme file, please let me know if you have any comments

[lggruspe]

I think this extension requires linking to math.h:

#cgo LDFLAGS: -lm

[nkt-dk]

Thank you for the feedback, I think you are correct. I updated the PR and added the linker flag

[rittneje]

Please also update the GitHub merge gate to include this new tag in the "Tags: full" step. https://github.com/mattn/go-sqlite3/blob/bedc2985efda510946f102c1e2a5595be070a2b7/.github/workflows/go.yaml#L46-L47

It would also be helpful to include a unit test (with the same build tag) to verify that the SQLite math functions are compiled in. I don't think it's necessary to cover all of them, just pick one to ensure the build options are being set properly. https://www.sqlite.org/lang_mathfunc.html

[bearbin]

@nkt-dk Just giving you a ping on this, would be good to get the build flag in sometime :)

[nkt-dk]

Hi @bearbin, I did not have much time lately but @lggruspe continued this fix and create a new PR here: https://github.com/mattn/go-sqlite3/pull/1059 Thus I think my PR can be closed and we continue in 1059?

[rittneje]

superseded by #1059