doc: add note about pmemlog_appendv()

Ref: pmem/issues#19
log: pmemlog_appendv: add assert on iovcnt

Ref: pmem/issues#19
Merge pull request #84 from ldorau/log-fix-pmemlog_appendv

log: fix pmemlog_appendv() if iovcnt is less than 0
vmem: enable limited fork support

Support for creating pools after fork.
Merge pull request #83 from spawlows/vmem-fork-support

vmem: enable limited fork support
common: fix cstyle to detect void pointers errors
Merge pull request #85 from plebioda/fix-cstyle-void-ptr

common: fix cstyle to detect void pointers errors
common: add requirement for unlimited virtual memory

Some tests fail if overcommit is disabled and virtual
memory is limited due to large memory requirements.
Such tests can require both overcommit enabled and
unlimited virtual memory.
blk: reduce the minimum BTT size to 16MB

Reduce the minimum BTT size to 16MB
and the libpmemblk minimum size to 16MB+8KB.
Update two unit tests.
Merge pull request #88 from ldorau/blk-reduce-the-minimum-BTT-size-to-16MB

blk: reduce the minimum BTT size to 16MB
Merge pull request #87 from plebioda/fix-overcommit-memory-issue

common: add requirement for overcommit memory in unittests