Conflicts:
	src/cell.c

Star formation sub grid update

See merge request !803

No cooling limit

See merge request !798

Make plots nicer in plotsolution and add temperature histogram, also change function call in star_formation.h to get the entropy floor

Cell flags

See merge request !792

Conflicts:
	src/cell.c

Mark the flags `volatile`, just to be safe. This is not a problem now, but I would hate it to become one later.

Subcell recursion

See merge request !788

Do not force the star particle to be a constant in the default feedback model. This is used for debugging.

Feedback restart

See merge request !800

Update the Rho vs sfr plot

Closes #575

See merge request !799

switch to using a 32-bit flag field and atomics, replace '|=' with '= ( ... || ... )', which should do short-circuit evaluation, and is easier to read.

Don't pass enums in the `cell_*_flag` functions, but rather use the type of the `flags` value itself. Using the enum causes problems when passing the union of more than one flag.

Dump and restore the space globals

Closes #574

See merge request !797

Update the brute-force debugging star interaction loops used in the unit tests to also check for feedback activity.

Also remove space_subsize_pair_stars & space_subsize_self_stars which are not used and a couple of typos

Make sure the EAGLE feedback conserves energy and momentum.

See merge request !793