fix #7739. for addprocs, this makes dir always specify the starting working directory (defaults to pwd()) and makes exename always specify the julia binary to run (defaults to $JULIA_HOME/julia)
docs: Fix indentation error
docs: fix spelling and formatting errors in parallel-computing
docs: fix duplicate label error
docs: Cross-reference parallel computing manual
docs: Crosslink package docs
Docs: cross-link linear algebra chapter
Docs: cross-link, fix formatting and grammar in network/streams
Docs: cross-ref performance tips
Docs: cross-ref variables-and-scoping
Docs: cross-ref types chapter
Docs: cross-ref style guide
Docs: cross-ref strings chapter
Docs: cross-ref shelling out chapter
Docs: cross-ref metaprogramming chapter
Docs: cross-ref mathematical ops chapter
Docs: cross-ref numbers chapter
Docs: cross-ref functions chapter
Docs: cross-ref FAQ

Also fix Markdown syntax in blog post link.
Docs: cross-ref dates chapter