Write an fslock wrapper with a Guard.

Right now the fslock crate has an LockFile object that can exist in a locked and an unlocked state. That makes it not-so-suitable for use cases where we want to ensure that the lock is held whenever a given piece of code is entered and/or for as long as a given object exists. To solve that, I'm thinking of making a LockFileGuard type that behaves more or less like MutexGuard.

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Bikeshed time: should there be data inside this type?

// OPTION 1:
impl FsMutex {
    pub fn open(path: &Path) -> Result<Self>;
    pub fn lock(&self) -> Result<LockFileGuard<'_>>;
    pub fn lock_owned(&self) -> Result<OwnedLockFileGuard>;
}

// OPTION 2:
impl FsMutex<T> {
   pub fn open(path: &Path, data: T) -> Result<Self>;
   pub fn lock(&self) -> Result<LockFileGuard<'_, T>>;
   pub fn lock_owned(&self) -> Result<OwnedLockFileGuard<T>>;
}

Also, do you prefer FsMutex, LockFileMutex, FsLockMutex, or....

cc @Diziet