Small documentation clarifications

See merge request laiser/caisar!96

Split task goal only in presence of datasets

Closes #40

See merge request laiser/caisar!93

Avoid splitting when not necessary as it may incur in performance hit. Indeed,
splitting means more (tinier) goals to verify, hence more call to provers.

    Biggest positive signed int32 is used when a node as no parents.
    It can't be represented in an integer in ocaml 32bit
    since they have only 31bit.

[aimos] Set CWD from CAISAR

See merge request laiser/caisar!95

Release 0.2

Closes #35

See merge request laiser/caisar!94