Support https with server certificate.

* Support parsing of is_folded bit

* Include folded bit lin (*Location).string() and in profile mergining

* address comments

* Set IsFolded to false during symbolization when Line is reset

* simplify tests

* Improve POST URL status error

* Mirror the connection error string

* Stop treating -symbolize=force as the default

The code parsing symbolize options was treating the empty option as
"force", effectively making -symbolize=force the default. This would
unnecessarily symbolize profiles that were already symbolized.

* Add more testing for symbolize option parsing

Do all parsing of symbolize options on a single function and
do more thorough testing of it.

* Have symbolz honor -force

Currently -symbolize=remote will force remote symbolization of mappings
that already had mappings. Making that depend on an explicit
-symbolize=force to make it consistent with local symbolization.

* Applied fixes from latest review iteration

* Add comment on symbolz check for resymbolization

* Reformatting comment

* Recognize (again) https+insecure scheme for symbolization POSTs.

This reverts the revert of #111 relaxing the test to make it pass as the
issue reported in #111 is caused by unrelated #120.

Added a test, verified the test failed before the fix.

This fixes #94.

* Fix the staticcheck failure.

Added a test, verified the test failed before the fix.

This fixes #94.

Fixes executables named on the command line on Windows.
Fixes the build failure on https://go-review.googlesource.com/#/c/36798 patch set 6.

Upstreaming change from golang/go@39366326.

HTTP body will be read and displayed when both conditions are true:
* Response includes non-empty header "X-Go-Pprof".
* Content-Type is text/plain.

The local symbolization already skips these mappings. Have the helper
which can be used when alternative symbolization flows are used.

The common mechanism to locate the main binary has several drawbacks:

- The identification of the main mapping is done through heuristics
- It can only override the main binary

PPROF_BINARY_PATH is a more robust mechanism, but it isn't widely known.
Add a message when symbolization fails recommending its usage.

Even after local symbolization completes successfully we should
call remote symbolization in case there are some mapping that couldn't
be symbolized otherwise.

Add some tests to ensure both local and symbolz symbolization are called.

When the source is remote and a mapping doesn't have either build ID or
file field set, the file field is set to the source URL so that the
proper source from the source mapping is used during symbolz processing.
Before this change, the file field would continue to point to the URL
producing the URL in pprof output which confuses users.

With the change it resets the file field back to the empty string. It
also now skips the URL-like paths during local symbolization as
reading at that path is not going to succeed.

We discussed switching to generating more unique IDs. On the second
thought, I propose leaving these to be URLs as that seems unique enough
and in case this field leaks into the tool or log output seeing the URL
seems still friendlier than some arbitrarily prefixed string.

When reconciling samples, cleanup file paths to allow functions to be
combined if their source filenames match after cleanup (eg "src.cpp" and
"./src.cpp").

Also clean up existing uses of filepath to avoid passing empty strings
to it: filepath.Base("") returns "."

Instead of including it the demangle package with pprof,
point to its own repo.

Also update the build instructions to use go get