Allow managing pkgset under local folder.

While replacing pakcageset name with "--local", the packageset
information will be managed under some/local/repo/.gvm_local folder, and
add the root path of repository as the first path in GOPATH and PATH.
This makes the repository more portable since we don't store all the
go-installed package files under $HOME/.gvm .

The repository root path for gvm is definded as $PWD while
"pkgset create --local" . When "pkgset list" under some configured local
repository, it will list the root path as the first packageset, and
marked with "L".
Update README.md

Better Go installation docs
Update README

Better Go installation docs
add -w option to grep
Merge pull request #20 from t-k/grep-with-w-option

add -w option to grep
Change response to already installed version.
Fix issue with running update source but then not properly finding version. () <= subshell fail
Merge pull request #18 from COLDTURNIP/master

Store packageset data under local path.
Provide support for vendored native code workflow.

This commit introduces generated overlay filesystem support for
${PATH}, ${LD_LIBRARY_PATH}, and ${PKG_CONFIG_PATH} as well as
includes a working example of how to take advantage of this support
when integrating with vendored code.
Merge pull request #21 from matttproud/feature/native-code-support

Provide support for vendored native code workflow.