Fixes #524

Co-authored-by: Alexey Alexandrov <aalexand@users.noreply.github.com>

Provide more helpful error message and require input for every non-bool option.

Fix comments according to best practices by effective go

Signed-off-by: CodeLingo Bot <bot@codelingo.io>

In the interactive mode, inform users of different sample types
if the profile includes zero samples for selected sample type
by default (or through user-provided sample_index flag value).

The example output may look like

$ pprof mem.prof
Type: inuse_space
Time: Mar 20, 2018 at 11:36am (EDT)

No samples were found with the default sample value type.
Try "sample_index" command to analyze different sample values.

Entering interactive mode (type "help" for commands, "o" for options)
(pprof)

Update golang/go#24443

* Add support for tag units

Updated tests for adding tag units

* updated proto docs to describe tag units

* fixed formatting

* added additional test

* require specific units for graph tag to be recognixed

* updated tests and formatting

* Fixed formatting

* Fixed style error

* modify proto_test to be sure tag units not overwritten

* Clarified label docs

* call legacy profile memory allocations size, not byte

* updated tests to call bytes tags in legacy profile size

* Revert "updated tests to call bytes tags in legacy profile size"

This reverts commit 9289378af2.

* Revert "call legacy profile memory allocations size, not byte"

This reverts commit 6b18973562.

* Updated so units not modified when profile written out

* Fixed formatting errors

* Removed field for inferred numeric label units from profile

* Modified profile String() output

* fixed formatting error

* changed name of function used to identify units for numeric labels

* Refactor String() for profile

* Modified for clarity and address comments

* renamed function for clarity

* Made numeric label units field seperate in profile

* Modified test

* Refactored identifyNumLabelUnits()

* Updated comments

* Fixed formatting error

* Addressed comments

* Fixed style error

* clarify comment

* Refactored to address comments

* addressed comments

* addressed comments

* addressed comments

Support commands like "top10" or "web5"

Rather than print options on each prompt, add a "options" command
that prints the current options in a user friendly format. Also,
make sure that those options can be parsed back as printed.

Currently pprof will look for source files only on the current directory
and its parents. This makes it hard to examine sources on jobs where
there are multiple source trees (eg from different libraries).

Add a variable to provide a search path for source files. It will default
to the cwd, so there will be no change in behavior by default.

Add field for profile sources to indicate what is the primary
sample value, which visualizers should display by default.
Previously there was a convention for pprof to use the last
sample_index by default, this provides more flexibility.

Also update the build instructions to use go get