uSync 17.5.2 and 18.2.1 released

Repo: KevinJump/uSync

Released uSync 17.5.2 to NuGet, with the v17.5.2 GitHub release. Supports Umbraco 17.3 to 17.8
Released uSync 18.2.1 to NuGet, with the v18.2.1 GitHub release
Both: culture and segment limited exports keep the right values. Invariant items no longer lose their values, cleared culture values now sync, and values from other cultures or segments no longer leak in (#1183)
Both: partial exports only stamp DefaultValues when they contain the shared values (#1180)
Both: items with a clean marker stay in the import order, as deleting at the root could stop them importing (#1182)
Both: export all skips content outside the Include paths (#1176)
Both: SignalR respects client negotiation settings (#1169) and blueprint folder names can contain spaces (#1153)
v18: the uSync API now uses the uSync section policy, so a user without that section can't call it (#1157)
v18: member type compositions now import (#1149)