loadtxt/savetxt: do not require space after last entry

[perazz]

Attempt to address #862.

The current formats require an end-of-row space both in savetxt and loadtxt, i.e.,

format(*(i0,1x))

This PR proposes to not require a space after the last record, i.e.,

format(*(i0,:,1x))

This should hopefully improve the seldom crashing CI tests.
@fortran-lang/stdlib @chuckyvt @minhqdao

PS: these routines would benefit from some form of error control in the read and write statements.
Without changing the API, I propose checking for iostat and iomsg, so that when something goes wrong, an error can be produced to give information about what happened (what file, which line).

[jvdp1]

Thank you @perazz . Pending minor comments, LGTM.
Note: I thought that write(*,'(*(i0,1x)') would not result in a line with a space at its end. Is this compiler-specific?

[perazz]

Is this compiler-specific?

I'm never sure about these string formats, so I went test it here. It seems like all most used compilers do add a space at the end. After this PR we will have an error message, so if those tests fail again, we will hopefully know why (I've never had any errors testing on my machine locally).

[jvdp1]

Can this PR be merged, @perazz ?

[perazz]

As there have been no further comments, I will merge @jvdp1. Thanks for the review and approval.